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What does water smell like? Did bipedal dinosaurs get back pain? Is my perception of time related to my heart rate? Does getting fresh air when you're sick actually doing anything? Are orange peels airtight? Why can't I smell ants? Why can't humans drink river water anymore? Deboki Chakravarti and Hank Green have answers!

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 (00:00) to (02:00)

[intro music by Gunnarolla]

Hank Green: Hello and welcome to Dear Hank and John!

Deboki Chakravarti: Or, as I like to think of it, Dear Deboki and Hank.

H: It's a podcast where two brothers -- and sometimes two friends -- answer your questions, give you dubious advice, and bring you all the week's news from both Mars and AFC Wimbledon. But probably not Wimbledon today. Deboki. You know why bacteria are so bad at math?

D: No.

H: Well, lemmie give you a hint. Do you know how a bacterium would multiply?

D: It would divide...

H: Can't do it that way! Can't multiply by dividing!

D: [laughs] I got it. I got it. It took me a second. I was mostly worried that I was going to be wrong about bacteria. My impulse any time anyone asks me a question is like, "I'm gonna be wrong, so..." I'm on the right podcast.

H: [overlapping] Oh no! Yeah, it's a huge problem when you're the science guy. And it's like, when you get something wrong. Like, well. Let's just all admit that everyone's fallible. And that also sometimes I totally forgot the difference between a prokaryote and a eukaryote.

D: [laughs] It happens.

H: It happens. It doesn't happen as much since we started doing Microcosmos. [laughs]

D: That's true. That has helped me. I think I realized how little I knew about microbes ever since I started working on Microcosmos. But then also working on Microcosmos has helped me realize how little everyone knows about microbes.

H: Yes! Yeah. We were like, "We'd like to make a video about this thing." And it's like, well, enjoy your two-minute long video. 'Cause that's everything humans know about it.

D: Yup. Exactly.

H: So, for people who... you've heard Deboki's name, at the very least, in the credits of this podcast because Deboki is our editorial assistant. Which means that she looks at questions and then we... [pauses]

 (02:00) to (04:00)

H: Every week before the podcast Deboki and I talk about science questions. To pick out which ones I might answer. And Deboki does a bunch of research to see if may there's something interesting to say about these topics. And during those phonecalls we make a podcast for just the two of us that I find very entertaining.

D: [laughing] It's very good. And moves fast. And we get through, like, two questions by the very end.

H: [laughs] We're like, "This! Can't! Be! Right!

D: Yeah.

H: There's a lot of it. Someone must have done this study before! Someone must have blindfolded a dolphin and taped its mouth shut and stuck a fish in to see if they can smell somehow.

D: Yes, that is a conversation we just had.

H: [overlapping] We just had. And also Deboki works on a bunch of other stuff. Hosted Crash Course: Organic Chemistry and works on Journey to the Microcosmos YouTube Channel. And is the host of the Tiny Matters podcast. Which you can also listen to probably in the very app you're listening to this on, if you'd like a little bit more of that. I'd guest-hosted recently so you can go listen to my episode.

D: Yeah, it was a lot of fun. Hank answered my questions for once so it was a good time.

H: [laughs] Yeah. So we've got a bunch of science questions and it's just science day. That's what we get to do today, here on Dear Hank and Deboki, because that's what we're good at. And we don't have John here to, like... um. Analyze Huck Finn or whatever.

D: Yeah. [laughs] Yeah, I can't do that. I could try, but that is not my area of expertise. But blindfolding dolphins...

H: Yeah, definitely. I'd be like, "I could tell you what Mark Twain would do if you blindfolded him and put him in a pool." 

 (04:00) to (06:00)

H: How did we meet? Just 'cause you're a YouTuber?

D: Yeah, I think just because I started working for you. I think that's what happened. [laughs] I think the first time we met was when I interviewed for this job.

H: Yeah, but I had known of you before then, probably because of Nicole.

D: Yeah, probably because of Nicole.

H: And just, like peripherally through that. Nicole is a producer on Crash Course who was also a YouTuber. But in quotation marks. Like, what was a YouTuber -- or is a YouTuber -- anyway? Made YouTube videos.

D: Yes, we do things that YouTube has managed to take from us and put on... like, when I say "take from us" it's 'cause we gave it. [laughing] We gave YouTube our things and we're like, "Do with it what you will. Throw it into an algorithm."

H: Yes, I will sign the implicit license that every creator signs when they upload a video without knowing what you're signing. So. Let's get started here. And this first question is from... I think Mace? But maybe Macey [sp?}.
Dear Hank and Deboki,
How do you smell underwater? I just watched a clip from the BBC's The Mating Game about flatworms. And it says flatworms are blind but they find their way by smell. But how could you smell underwater? This also begs the question: What does water smell like? 

Smell ya later,
D: I like the "I wonder what water smells like." I feel like there's a touch of "what color is air" to that questions.

H: Yeah. Well. Air has a color.

D: I mean, does it?

H: It does! Do you wanna know?

D: Yeah.

H: I think that we've -- you and I -- have had this conversation before. If you would like to see the color of air go outside and look up on a day that isn't cloudy. What else is it? There's nothing there. It's just air.

D: Mmhmm. So just stick your head into the ocean and that is the smell of water.

 (06:00) to (08:00)

H: Sniff it up, and what it smells like is pain.

D: [laughs] Yeah, it would not smell good. Please don't do that, people.

H: Yeah, I mean, I'd assume we've had water go up your nose. The thing also is that your nose is always wet. There's always moisture in your nose. So just, like, the smell of air. The smell of wet has to be something that you just filter out. Or doesn't get detected.

D: Yeah, our brain has just ruled out whatever the smell of our own mucus is. Unless it's really bad, I guess?

H: [laughs] Yeah, we've all had a nose so we know sometimes, suddenly, there is a smell. Just a little one. And also every morning when you wake up. Gross! Bodies. The pain.... is because of osmotic pressure, I think. So, like, you put salty water up your nose and the salt will go into your nose, like across the cell membranes and if you put fresh water up your nose then the salt will come out of your cell membranes and both of those are unpleasant. But if you put the right salinity of water in your nose it's basically undetectable. Just like having snot in your nose, is basically undetectable. Except that it's warm, or whatever it would be coming out of your neti pot. Which... neti pots seem to be a bad idea, I don't know.

D: Yeah, I've never done it. And it scares me.

H: People keep having problems with it. So I just wanna not be an endorsement.

D: We're really hard on the non-endorsements right now. [laughs] Don't stick your head into water to smell it. 

H: Don't just, like, really deeply inhale a bunch of seawater.

D: Though I guess that is the question when you use a neti pot, can you smell the water in the neti pot?

H: I bet... oh gosh, I found out a fact! 

 (08:00) to (10:00)

H: So, I don't know if... have you ever had an IV?

D: Yes.

H: So, when you first get an IV, sometimes they will flush it with saline. They'll hit you with a syringe full of saline water. This is a little bit terrible, but it's true and so I guess we'll just live with it. Sometimes when that happens, patients will report that they can smell it. And that's very weird. That something is being put into your veins and then you can smell it. Especially because it's saline. It's just salt water. And so that's what, when you said, "Can you smell the neti pot water," that's what it made me think of. But you're not actually smelling the salt water. What is happening is that that saline was sitting around in that plastic syringe for a while, possibly quite a while, and some of the volatiles from the plastic dissolve in the saline. And then it goes into your blood, hits your lungs, evaporates into your lungs, and you breathe it out. I'd fact-checked this six ways from Sunday. It seems so wrong but it is the correct... and if you prep a saline flush and then use it immediately, this smell does not happen. It only happens with plastic syringes that have been sitting around for a while.

D: Wow. Oh wow. And so, like, they've been able to... do you know, like, were people tracking these compounds? Were they measuring what was coming out of people's mouths?

H: No.

D: But they know that this is the thing.

H: Yeah. Yeah, yeah, it was like, any nurse will have heard this from their patients. That some patients... and not everyone notices it. But there's this sweet smell from getting the saline flush. Which, I told that to... I get a regular infusion for my colitis and I told that to my nurse and I came back in recently and she was like, "I've been telling everybody!"

 (10:00) to (12:00)

H: And I'm like, "You shouldn't do that in this town! People hate plastic in this town!"

D: [laughing] Yeah. I hope she's citing you. I hope everyone is like, "That is my Hank Green fact for the day."

H: Uhhuh. She was like, "Are you the one who told me?" And I'm like, "I am. That was me. That's what I do for a living. I tell people facts. "[laughs]

D: [laughs] Yeah. Once you start, you just can't stop. "You guys have to learn about this horrible thing I learned."

H: Yeah, they did this study ages and ages ago. I don't know, it was like, 10+ years ago and hasn't spread around. And I think it's because people don't wanna say it. It's like, you don't wanna eat out of a plastic thing you microwaved it in because it might taste plasticky.

D: But you said it was a sweet smell?

H: It kinda smells sweet, yeah.

D: Huh. So it's not too bad.

H: No, it's not. But I am like, "I dunno if I want that stuff in me." I guess it evaporates quickly, otherwise you couldn't smell it.

D: Yeah, if it's happening pretty fast, it sounds like?

H: Yeah.

D: Weird.

H: So weird.

D: Bodies are so weird!

H: So weird. [laughs] But! So I'm confident that I can't smell underwater because I'm not set up for that. 

D: Yeah, you're not. Probably.

H: But, like, flatworms. What you mean by "smelling" is basically tasting. 

D: Probably. I was looking up what their organs are. I think they're supposed to have some little organs in their heads that help out with smelling. But I couldn't find too much more about how they work. But there are a lot of very fun animal smelling methods. For a while researchers thought that maybe mammals aren't great at smelling at underwater but they found some that are. So there's the star-nosed mole, which actually the way it smells is so cool. It blows bubbles out of its nostril and then sucks them back in to smell. [laughs]

 (12:00) to (14:00)

H: [laughing] Sucks them back in?! [laughs]

D: And they were able to use this to follow earthworms and fish scents.

H: Are they underwater? They're underwater moles?

D: Apparently. Let's see...

H: I mean, I don't see why not.

D: I think they're still using -- at the very least I think they're doing this underwater. They're semi-aquatic and found in low-elevation areas. So yeah.

H: Living their underwater lives. That makes sense! And so they blow the bubble but they don't let it escape and float up. They suck it back in. They probably do that a bunch of times. And then whatever is in the water is evaporating into the bubble and then they can detect that.

D: Yup. Which is so cool! I think that is so weird and so cool.

H: I guess if you wanna smell the water that's what you have to do, you have to go [makes snuffling noises]. Really little ones.

D: Or, like, if you're a shark apparently they have these nasal cavities - I think they're called nares -- and so one side of the nar[is] is for pulling water in and the other for's letting the water go out. And it's like, along the passage it passes these sensory cells and that's how it smells and processes the water.

H: How are we distinguishing that from taste? Because if I put some Coca-Cola in my mouth and swished it around and spat it out. But I have to have it come in one side and then I'd spit it out the other side I'd basically be smelling like a shark.

D: True. I don't know. 

H: Is there, like... brain parts that are differently involved? Maybe.

D: That's my assumption.

H: It also might just be physiology. Where it's like, like, well is it using the nose holes.

D: Yeah. [laughing] That might basically be what it is.  'Cause this is, like... So part of the mystery is also -- and while we were talking about blindfolding dophins -- is there's this idea that cetaceans... [as an aside] Cetaceans? Whales and dolphins...?

H: Mmhmm.

D: They can't smell but in 2008 there was some kind of dissection of a whale that revealed some kind of olfactory bulb. So maybe they do?

 (14:00) to (16:00)

D: And so there's the question of how do we find out? How do we even know, are they smelling things? If we wanna test out...

H: Sorry, did you say what kind of whale it was?

D: Uhhhh, no, I did not... let me see...

H: It doesn't really matter, because no matter what it's gonna be really hard to tape its eyes shut and its mouth shut. And be like, "You can only smell!"

D: Yeah. I think it was a bowhead? It was part of a bowhead hunt. So don't think they're gonna be doing that willingly.

H: [overlapping] But their nose is their blowhole. And I feel like they're not breathing in through their blowhole. At that point it's just tasting. We also --

D: [overlapping] What apparently it was is they're not smelling underwater so maybe it's just when they're coming up in the air? SO maybe that's the difference? So they can smell but maybe it's not -- the trick is that it's not underwater?

H: We also found a study where they took dolphins and put a stinky fish bucket and a not-stinky fish bucket and measured how much they sniffed the stinky fish bucket. But that was also out of the water. So it was like, yes, they are using their blowholes to smell with. But not underwater. I love the idea of imagining a dolphin like a dog. Where it's just got its nose down in the ground and it's like, [makes sniffing noises] Except it's on the top [laughing[ on the top of its head. And it's just trying to sniff a stinky fish bucket.

D: Yeah, it's looking. It's trying to find out where that smell is coming from. I think that's the way we test out how they're able to smell. But like you said, we don't know. Are they tasting the water? Are they smelling it? What's going on? I don't know.

H: Well, it does make me kinda feel like I just have one very bad nose, and it's my mouth. And one very good nose, and it's my nose. 

D: Which one would you rather do without? If one had to be... blind ... to what it's doing?

 (16:00) to (18:00)

H: Oh, okay. I was like, "I need my mouth." [laughing] You can't just take away my mouth. I need that. The nose is basically a backup. I think that I'd rather lose my... [dithers unintelligibly] I don't know!"

D: I guess that's where it gets confusing 'cause you're like, "If I lose the sense of taste in my mouth do I still have a sense of taste through my nose?" 

H: Yeah, I think that you would but you wouldn't get that, like big, good, strong, taste thing. Which is the overwhelming salt-sweet-bitter-sour-umami. Thing. Which is very good.

D: This is why bodies are confusing. They're so complicated.

H: I'd have to think about it a lot if there was some kind of all-powerful alien who wanted to just make my day bad. [laughs] Be like, "I'm gonna take away one!" I'm like, "Why??" And they're like, "I don't know! This is... I'm the alien that does the hypotheticals. They made me this way."

D: [laughing] The alien that does the hypotheticals. That's the job title.

H: [laughs] But flatworms, do they just have an organ that detects chemicals in the water?

D: I think so. I think that's the way they work. So they're just processing the chemicals. [pauses[ Yeah, until maybe the person's asking do they become noseblind to the salt part? I assume so. I assume at some point if you're living in the ocean your brain doesn't process the salt as part of that.

H: Yeah, I think that there's an evolutionary advantage to not thinking that the normal baseline environment has a smell. Or is even detectable. You only detect deviations from the baseline.

 (18:00) to (20:00)

D: Different organisms, especially if you're talking about organisms that like living in salt water, do they need an optimal salinity? 

H: [overlapping] Sure, sure. Yeah, like some kind of salinity detector. 

D: [overlapping] There is kind of an adjustment there, yeah.

H: Uhhuh. There's probably some -- like, if you're a saltwater fish and you're entering an estuary you'd be like, "Ugh, this does not taste... This taste is different." But have you ever been swimming in the ocean and then drank fresh water?

D: Probably.

H: So this is a thing that I've noticed as a Florida boy. When we used to go to the beach we'd be at the beach all day. And then you'd go to the little shower at the side of the beach to get all the sand off you. And when the water would go in your mouth from the shower it would taste sweet because you had had so much salt water in your mouth all day.

D: Ohhhhh. 

H: Additionally I'm wondering if -- what is the daily dose of sodium if you spend all day in the ocean? People worry a lot about, like, I don't wanna have too much salt. I can't have an extra bag of potato chips, or those fries. Or I'll get the low sodium Tostidos. But you gotta eat a lot of salt when you're at the ocean. It's all salty. [laughs]

D: Do whales have heart problems 'cause of the salt? [laughs] Do they need the low-sodium ocean?

H: [laughing] I think the whales have it figured out. I think they evolved their way out of that problem, but not us. I'd like to know! Yeah, how much... I feel like somebody has to have done a study to see how much, on average, a surfer consumes of sodium in one surf session. Maybe it's not that much. It's not like you drank it. 

D: Yeah.

H: Alright, this next question comes from Jenna. Who asks:
Dear Hank and Deboki,
After watching Hank's recent video about back pain I have a question. Did bipedal dinosaurs ever get back pain? 
Pachycephalosaurus and Protarchaeopteryx,


 (20:00) to (22:00)

H: I feel like I did great on that second one.

D: [laughs] It was perfect.

H: Did dinosaurs ever get back pain....? I know that we can sometimes see evidence of different disease[s] in fossils. So I would be surprised if there was no dinosaur we ever found that had some evidence of, like, arthritis in its back.

D: Yeah, so... there is -- not a bipedal dinosaur but -- there was a dinosaur called a phytosaur, which apparently is crocodile-shaped, where they--

H: So crocodile-shaped but not a crocodile. Because crocodiles...

D: No. Um, and so they found spondyloarthritis so that's bone mass growing between the joints. So that probably hurt. But otherwise the main thing that maybe they could have back pain is that researchers were looking at Tyrannosaurus and they found that they had intervertebral discs -- 

H: [overlapping] Ohh! Just like us!

D: Yeah, like us. So that's not like reptiles. Reptiles are more like the ball and socket joints like our hip joints. So this was kind of a surprise but does that mean that they hurt their back? Does it mean that they had a herniated disc? We don't know. [laughs] We don't know what that would look like for the T. rex. Or maybe we do but we haven't seen it yet.

H: Well, I mean, there were a lot of T. rexes over a long period of time. There was no T. rex that didn't get a herniated disc. Some T. rex at some point had back pain. It was definitely not as common as it is in people. 'Cause we are terrible at having backs. It does make me wonder about, like, Apatosaurus. The big long neck boys.

 (22:00) to (24:00)

H: It seems like a lot!

D: Yeah, it does.

H: It seems like a lot to work through.

D: And like, if you wake up with a bad neck one day but that is your entire mode of survival. [laughing] Like, what do you do?

H: [laughing] Wake up with a bad neck but you're a dinosaur that's almost all neck.

D: Like, do giraffes get little tricks in their neck?

H: I mean, giraffes neck fight. Which is wild. 

D: Agh! That just seems so painful.

H: [laughs] Yeah, they whack each other with their horns on their necks. I don't know, man. It seems like if you can get up to that level of nonsense they're probably pretty sturdy. 

D: [laughing] Well we got to this level of nonsense, and how sturdy are we?

H: [laughing] We get up to so much nonsense, yeah. I bet, again--

D:  [overlapping] Like, how weird would dinosaurs think we are? Like, would they look at us and be, like, "How do you guys function?" Right?

H: Yeah, I mean, there is no doubt in my mind that every single conscious organism would find any other species of conscious organism just so entirely, perfectly, absolutely bizarre. "No way you're like that."

D: "How do you live like that?"

H: "Are you serious? You put your wet face hole on the other's person's wet face hole, and that's like, great?? That's, like, one of your favorite things about life? No."

D: [laughing] I mean, I spent the weekend watching dogs sniff each other's butts. That's all I have to offer. It's like, "We don't do that!"

H: That's probably extremely normal -- like, that behavior, to us, is way more normal than whatever we do to aliens. But no, I can't really see being a species that sniffs butts for a living.

 (24:00) to (26:00)

H: I will gladly skip that.

D: Yeah. But I think back is probably just a way of life for a lot of animals.

H: I mean, one thing I definitely know is that everybody's got pain. There is kind of not a nice way to go out. Naturally. So... Everybody's got pain. Especially at the end.

D: Yeah, I don't have a joke to add to that. [laughs]

H: I appreciate you not putting a joke on the end of that one. Do we know much about dinosaur injuries more broadly?

D: Yeah, so I did find a paper that was very fun to look at where they were just like, "What do these fossils tell us about how dinosaurs have gotten hurt?" They documented percentages of things that were injured. Like, 25% of injuries were to the upper limbs and shoulder girdle. And I just really like the idea of this, like, table existing that's just like [laughing], school nurse for dinosaurs. "These are the injuries they got." Yeah, so there are stress fractures that they're like, "...can be caused by repeated sudden forceful movements such as leaping to escape attack or grappling with powerful prey." And like, I just imagine that's what most of their life is. I think that would just be hard.

H: I'm glad I'm not a dinosaur. Any kind. I bet it would be bad to be every kind of dinosaur. [laughs] Okay, next question is from Luke, who asks:
Dear Hank and Deboki, 
Is my perception of time related to my heart rate? 
Moderately warm,
H: [laughs] I don't know if you're asking this because of the study, but I just saw a study published about this. Like, a week or two ago.

 (26:00) to (28:00)

D: Yeah, I remember seeing this too. And, like, immediately thinking of it when I saw this question. Because basically researchers at Cornell, they hooked up some undergrads to electrocardiograms to measure the length of their heartbeat. And then also had a tone set up that would -- so it was a computer hooked up to the electrocardiogram as well that would play a tone when, like, I think when the heart beat...? Or something? And so basically... So researchers at Cornell, they hooked up undergrads to electrocardiograms to measure the length of their heartbeats and they also asked them to estimate the length of these audio tones. And so there was a correlation between a lower heart rate... was connected to a, I think, I longer....? Sense of time? It was kind of confusing to understand whether it was the length of the heartbeat or the heart rate. I was trying to read a few different things and each article and press release kinda phrased it differently? But my understanding is that basically, yes, your heart beat is related to the way that you estimate time and you understand time.

H: That's weird! And this is all -- There's been a lot of hemming and hawing about the perception of time. Especially in high stress situations, that it seems like time slows down. And then there's a... yknow, like, "Time flies when you're having fun!" That's definitely true. And time goes very slow when you're very bored. That's quite easy to measure. I love laboratory studies about boredom. 'Cause people sometimes say that they don't get bored. Like, "I never get bored!" But, like, scientists can induce boredom so easily. They have procedures for it. They've got, like, games that they're like, "You have to play this game." 

 (28:00) to (30:00)

H:  And the game is just... so. Bad. It's like a computer game and you have to just do the same thing forever. And it's like, people are like, "I hate this a lot!" And it is not-- like, I don't know, there's something else to it. I don't remember exactly. But I just love the idea that there are known protocols for inducing boredom. Boredom scientists use the same technique every time so that they can have [laughing] comparable research. [laughs] Just, like, standard boredom induction.

D: I hope that they messed up the first few times. And it was like, [laughing] "This game is still too exciting! They're having fun!"

H: [laughing] "I'll do this!" I mean, I've played some games that are just me doing the same thing over and over again forever and I, like, for some reason my brain's like, "Yeah! That seems different!"

D: [laughs] Every time I play the game of Life I do the exact same thing. [laughing] And I will, like, go for the same cards. Like, I haven't even played it in a long time and I know exactly what I would do.

H: [overlapping] For a second I thought you just meant just, like waking up in the morning. And doing your day. [laughs]

D: [laughs] Yeah, I pick out the same cards every morning! From my nightstand. "These are my day cards today!"

H: Maybe I should have a bunch of cards on my nightstand that'd be like, just pick out which one I'm gonna do today. Be like, "Today: must call a friend. Today you must... walk outside for your stupid mental health! Today... Today you must... eat a corndog." And I'm like, "Ah, thank you, cards."

D: I think that's what astrology is. I think you just wake up and you let the horoscope tell you. Tell me what I gotta do today.

H: [overlapping] Tell me what I should be -- It's like, "Be very careful going on the stairs!" I'm like, "Alright, card! I will!" That's probably for every day. Should always be careful going down the stairs. I'm 42 years old and I got bad ankles.

D: That's what you need the cards for. [laughs]

 (30:00) to (32:00)

D: [laughing] They're like, "Today's the bad ankle day."

H: [laughing] Yeah. Please tell me. Did we answer this question?

D: I think so. I think yes. Your perception of time is related to your heart rate. My perception of how is dependent on who wrote the article I'm reading.

H: [laughs] 45 participants monitored with.. oh. 

D: [laughing] Oh, sorry, ECG.

H: ...electrocardiogram, but Deboki wrote in the notes "EGG."

D: But imagine if it was an egg.

H: [laughing] How did eggs get involved?? Is this a separate study where they had to do something with an egg?! 

D: Maybe it's like an egg timer. Sorry, that-- and then EGG was connect-- in the next slide the same of type-- I think it's an autocorrect. "EGG is connected to a computer." [laughs] Man, this was a great experiment.

H: Alright, another question. It's from Ray, who asks:
Dear Hank and Deboki, 
When I'm sick and my mom tells me to go for a walk and get some fresh air, does this 
do anything? Or is it just a saying that comes from when we knew a lot less about illness? I know that John has mentioned TB spreading out to the American west when doctors sent people there for "fresh air." But that obviously didn't cure it. Is there some real science to "fresh air" as a cure? 
Not just somethin' you say,
H: I'm gonna venture a guess. That it can't hurt.

D: Yeah, I think that's sort of the gist of what I got. I think at the very least ventilation is good for you a lot of time. We saw that with COVID where having air flow was just generally a good thing. So I think that's a big part of what fresh air does for us, especially if a lot of us -- like, I spend all day at my desk and I feel like when I got outside after a long day at the desk I'm like, "Oh!" Feel like I can breathe again.

 (32:00) to (34:00)

H: Yeah, there's a wild amount of science about this, actually. Building ventilation. And the fluid dynamics of air moving throughout a building is kind of a really big deal and it is a part of how engineers -- Shini Sarmara who did the Crash Course: Engineering series studied air movement in buildings in her engineering degree.

D: That's so cool.

H: There can be areas where air -- the ventilation kind of doesn't reach it. And so it gets very stagnant and can have a buildup of carbon dioxide from people, but also VOCs from carpet or paint or other off-gassings. And so it's less healthy air and you gotta hit all the cracks with your ventilation strategy. Wild. So carbon dioxide is a big one and it is just good to get out of the house and into the norm-- like, your house will always an elevated level of carbon dioxide because it's got people in it and it's, y'know. Sealed from the outside. [laughs] It's [unintellible] things you need for CO2 buildup. And that does just kinda make you feel better. But also it just feels better to get up and walk around. Even if you feel like just doing one lap around the block.

D: It's annoying. I find it very irritating that it works. [laughs] But it's like, "Oh, okay, I guess if it works it works."

H: When I had COVID I did not leave the ho-- like, I got COVID and I was in a hotel room. And I had to stay in the hotel room for, like, ten days. And I didn't leave the hotel room for that whole time. It was very bad.  

D: That sounds very difficult.

H: Nah, that's not the life you wanna live. But! DoorDash exists. So I had everything that Taco Bell has to offer.

 (34:00) to (36:00)

D: [laughs] Did you have a favorite thing from that-- like, what was the best thing you got from Taco Bell at that time?

H: I'll tell ya what. Taco Bell, DoorDash... don't... Anything crunchy is a no-go. Because it's gonna not be crunchy anymore. So that was a bit of a disappointment. But honestly my favorites remain my favorites, y'know? I like the chicken taco. I like the [speaks softly] bean burrito, which is gross

D: It's all good. [laughs]

H: I'm like, "I love this." When I was in high school I was very mad when they raised the price of the bean burrito to 39 cents. So that's how old I am.

D: [laughs] Now I'm trying to remember how much the bean burrito was when I was younger... But I can also imagine being upset about that. You didn't go to Taco Bell for price rates. 

H: [laughing] Yeah, yeah, this is supposed to be a 29-cent burrito and that's a normal thing to expect from the world. Oh terrible.  Which reminds me that this podcast is brought to you by the 29-cent bean burrito, only available in the mid-90s [laughing] at Taco Bell in Orlando, Florida.

D: This podcast is also brought to you by EGG. The source of all of your best experiments.

H: [laughing] This EGG.

D: Just hook it up! Hook it up to your computer right now

H: Podcast is also brought to you by dolphin blindfolds. Available on so you can do all of the different research that you need to do on your friendly neighborhood cetacean.

D: This podcast is also brought to you by the alien that does the hypotheticals. Like dolphin blindfolds.

H: He's so bad! I hate him! Oh god. 

D: Hypothetically, if you were stuck in a room for ten days and you had to DoorDash from one place.... [laughs] why did you pick Taco Bell??

H: [laughs] I wanted to be sad, y'know?

 (36:00) to (38:00)

D: Yeah, no, I understand. I think Taco Bell is a very good comfort food, especially in COVID times.

H: This next science-y question from our science-y Dear Hank and John archives is from Leo who asks:
Dear Hank and John,
I'm wondering if orange peels are airtight. I saw an orange in my dad's car while I was riding to school and I thought--

H: [laughing] You just said... yeah, no, okay. [laughs] That's a very funny story to me. To tell me right after you asked the question. Yes. You were thinking is it airtight around the orange.
[question continues]
I've been listening to the pod for about a year.
Ares, not a 

H: Are orange peels airtight? Well. Is anything?

D: Yeah. So.

H: [laughing] Important question.

D: What is airtight?

H: What is airtight? 'Cause there's some things in the air... there's a few things in the air that are much smaller than most of the things in the air. Those things will be less airtight to those things than the other components of the air.

D: Yeah. So I think I've decided that they're not airtight. I spent a... few different ways thinking about this. I was like, "Well, to start off with I think you can wash an orange. So it's watertight probably, right? I don't think the orange gets wet. Unless I'm wrong. But I think you're fine. 

H: I think you're right. I think you're right. There's only one way to find out.

D: Everyone watch your oranges right now.

H: Everybody just dunk your oranges in water and then... so, no. Here's what you have to do: you weigh your orange with a very precise scale, put it in the water, let it sit there for like, two to... no, that's not gonna work... It's gonna off-gas

D: [overlapping] Yeah, 'cause you're gonna have to let it... yeah.

H: There's gonna be all kinds of different mass things happening.

 (38:00) to (40:00)

D: And then, so the other thing that I was wondering about is whether or not ethylene gas is a part of orange ripening.  'Cause I was like, "Okay, so ethylene is the gas that is involved in fruits ripening. If it gets past the peel then we know that it's at least permeable to that gas..." But apparently citrus fruits aren't -- they don't really rely as much on ethylene, I think, for their ripening. People do use ethylene to make the color of the peels more even. So maybe there's that. But then finally I found this paper from 1992 that was comparing the gas permeable of fruits with wax coating. And they were looking at the permeance of them. So that's the actual variable they're looking at. And it turns out that an uncoated, non-refrigerated orange does have a non-zero permeability. It's 100,000-something whatever the units are. Milliliters per... meters squared times day times atmospheric pressure, I think, or something?

H: Ohhhhh! Okay.

D: And then that permeability does go down with a wax coating. So basically in some way I think there is something permeating the peel. And so they didn't specify what things would be permeating, but I don't think it's airtight.

H: I think it's air. [laughs] If it's atmospheric pressure, it's probably the atmosphere. Do you remember the actual number?

D: I think it's 100,000...

H: 100,000...

D: ...Yeah, just a very, um.... 

H: 100,000 milliliters? 100,000 milliliters... per meter squared... per day. That's a lot! 

D: Yeah. But that's a big-- meter squared.

H: That is a lot of orange. For sure. A meter squared is a lot of orange peel. 

 (40:00) to (42:00)

It occurs to me that you could determine if an orange peel is watertight in a very simple way, Deboki, and I'm ashamed that I did not think of making it into a little cup and then drinking of it. It's obviously water-tight. You can make a little cup out of an orange peel. And it's not gonna dribble out the bottom. But in the same way I feel like if I put an orange peel up to my mouth and try to blow through it I would not be able to.

D: You wouldn't know what's coming out the other side. Probably. Like, maybe.

H: But something would be. Some very small amount of gas probably would be. 

D: Yeah, I think it's not gonna be completely airtight.

H: And if my mouth was--

D: [overlapping] Can you use an orange peel as a mask? Can you breathe through it, either?

H: No.

D: Or would you be completely suffocated?

H: Yes. You could definitely be suffocated by an orange peel. I'm confident. And I'm gonna... [laughs]

D: [laughs]

H: [laughing] That's not what I meant! I wanna do the thing where you put the orange in your mouth. [muffled, as if he's biting into a peel] Where you smile and it's orange. [normal voice] And then blow really hard and see if I can breathe through it. And I bet you I will not be able to. But! If my mouth was one-meter square and I had a one-meter square orange peel, and I put my one-meter square mouth on that one-meter square orange peel, and I breathe -- I could breathe in 100,000 milliliters of air over the course of a full day. 

D: I think so.

H: Which would not be enough to survive. I'm sure that I breathe in way more than 100,000 milliliters of air a day. 

D: Yeah. I hope so. [laughs]

H: [laughing] I dunno how much, but I think it's more than that. I think it's more than 100 liters of air. Yeah.

D: [laughs] So this was not the point of the question, but yes. [laughing] Don't breathe through orange peels!

H: But, like. Yeah...

D: [laughing] I'm glad that we can give terrible life advice even when it's just science questions.

H: But what it really comes down to is it would probably seem airtight to us.

 (42:00) to (44:00)

D: I think so.

H: Like, you could fill and orange peel up with air and it would feel like it was squishy, like a balloon.

D: Yeah. I think so.

H: But then it would depressurize fairly quickly. Just like how balloons aren't actually airtight. Because they empty out eventually.

D: Do we know what the most airtight thing is?

H: [deep breath] What's... I mean, it's gotta be... just, like, an airtight thing but thicker. The space station? Metal? Like, a thick sheet of steel probably would be pretty airtight. Acrylic. Plastics are probably pretty dang airtight. It's probably really to do with the thickness. That's probably why balloons don't feel very airtight, because they're very thin. Stainless steel is the most durable material for airtight food containers. Like cans. Cans are pretty dang airtight.

D: So just wrap your orange up in a can.

H: [laughing] Bite into an orange and then just steel. Leo, I feel like we really helped you in this situation. The first thing we need you to know is that none of the words mean anything. "Airtight" is just something that's made up in your head. Air is so small. It can get through anything.

D: Tiny. Even an orange peel.

H: I wonder how much air leaks out of the international space station every year? 

D: [reading] ...rate of point six pounds of air per day...

H: Wow, that's a lot!

D: By August 2020 the problem had increased fivefold. Oh, so there's actually a leak.

H: There's a leak.

D: They used... [reading] Astronauts plug leak on the international space station with the help of floating tea leaves.

H: [fake gasps] "Everybody be very still! I'm gonna waste some tea! Don't make any... turn off all the fans!"

 (44:00) to (46:00)

H: They probably had to turn off all the fans, to see which way the tea leaves started going. I love that. I wanna watch the little miniseries.

D: Yeah, they have several photos and videos of the direction of the teabag's flight, or where it tended to fly, and this precisely shows the direction the air is blowing from the possible air leak. So yeah, they used the tea to figure out where it was and then they taped it. [laughs] As you would actually expect.

H: Then they got their spit on the leaves and just pushed it in there. I bet, though, that the space station would -- even if it were perfectly airtight -- still lose some air. By which I mean not perfectly airtight. But that would be a very good way to test. Because there's a big pressure differential in those two situations.

D: Sure is!

H: Though... There's bigger pressure differentials right here on Earth sometimes. Like in the boiler of a power plant. Way bigger than that. Alright, this next question comes from Vivian, who asks:
Dear Hank and Deboki,
Some friends and I were talking [H laughs] two of my friends mentioned how horrible ants smell. They said that ants smell like rotten cherry chocolate. I have never smelled an ant [pauses] voluntarily or otherwise. Why can some people smell ants? And why do I not smell anything?

A very importANT question,
H: Deboki, do ants smell?!

D: Yeah! Yeah, apparently. This is my favorite kind of Dear Hank and John question. 'Cause I saw it and I was like, "That's not a thing." And then I looked it up and it's like, "That's a thing!" Apparently ants smell like formic acid.

H: Suuuuure.....

D: And I don't know what formic acid smells like, and I don't know if you do?

H: No.

D: But apparently it's a thing that only some people can smell.

H: Whaaaaaaaaaat. Whaaaaat?

D: Yeah. So to some people apparently it smells like blue cheese. Other people, it smells like citronella. It's probably just a genetics thing, whether or not you're one of those... lucky, I guess? ...people who can smell it. But yeah, that is the ant smell.

 (46:00) to (48:00)

H: That's the ant smell. I mean, I've been around ants plenty. I've been -- formic acid is the stuff that fire ants put in your that burns and makes you itchy. So, I've... Trust me, I've had it in me before. But I've never smelled it. That's so weird!

D: Yeah, so I'm just so curious. For everyone who smells ants, like how many ants does it take for you to-- like, if there's just one ant around, are you like, "There's an ant"? Or... How many ants do there have to be for you to realize this?

H: Apparently it also smells vinegary, which makes sense with blue cheese. And it's only smellable by some people. Woowwwww. I love that. I also love the idea of just feeling like you're totally being gaslit by your friends. Where they're just like, "Oh, ants smell so bad." Like, "What are we gonna do to Vivian?  What are we gonna say?"

D: [laughing] Yeah. "You're not gonna trick me!" Yeah, I would totally not believe someone if they told me that ants smell, so. Apologies to all of the hypothetical people I didn't believe because, apparently, according to the internet, you're all right. And ants smell.

H: [laughs] Alright. That was an easy one. And this question comes from Nola, who asks:
Dear Hank and Deboki,
Why can't humans drink river water anymore? Like, chimpanzees, they got no problem drinking from natural bodies of water. So at what point in our evolution did we lose this ability to deal with whatever bad stuff is in the water? Do other animals have this problem, or is it just us?
Not the city,
H: Uhhhh. I'm gonna venture a guess that... well. I think there's a bunch of stuff going on here. But. Water-bourne pathogens are not just a problem for people.

D: No. [laughs] They're a problem for everyone. 

 (48:00) to (50:00)

H: I think that there are reasons why it can be worse for people. Particularly because we tend to live in really high densities of people. And so we can -- there could be there's more human pathogens going into the water source and so you're more likely to get it. But yeah. I mean, animals get... And there's all kinds of stuff that we're dealing with here. So there's chemical things that you don't want to eat that might be in water. That's probably the thing that, if you're just talking about river water, is not that much of a concern unless you're near, like, an old mine or something. And then there are bacteria. And there are parasites. And there are viruses. And there are single-celled parasites and eggs of bad things. There's all kinds of different things that can live in water and make use of your body. And those are the things to be worried about. And that is a thing that happens for lots of animals.

D: Yeah. And so, I think a parallel maybe to what you're saying in terms of human density, for animals I think the parallel to that is watering holes. So it's not quite river, but a lot of animals go to a shared watering spot. And so that does actually lead to diseases spreading between the different animals that are gathering there. But one of the things for animals is that they're going these rivers and these waters over the course of their whole lives. And so, over the course of their lifetime they're probably exposed to a lot of microbes at a low level so that gives them exposure. So that might help actually build up some of their immunity. So I feel like that sort of reminds me, like, for me -- I used to go to India every summer. And like, my family they grew up in India so they can drink the water in India. I cannot [laughs] drink the water in India without having problems. 

 (50:00) to (52:00)

D: So I don't know if this is a similar kind of mechanism. I assume it's kind of the same thing where you're exposed to that water over a lifetime where you've built up that immunity. Which is why you shouldn't try to just go do that now if you've grown up not drinking that water. You shouldn't be like, "I'm gonna get that fancy immunity now." But if you've grown up with it you might have that low-lying exposure. And yet at the same time you're still at a higher risk for a lot of the other things that are in the water just because it might have other stuff going on that you can't build that immunity to.

H: Right, yeah. Yeah, everybody is at risk but some people are at more risk. This is such an interesting topic that the-- like, there's a sort of meme that if you've never brushed your teeth you wouldn't have to brush your teeth. This is not true, but there is truth in it. So if you never brushed your teeth you might have a more broadly successful and competitive microbiome in your mouth. Where there isn't one species of bacteria that's doing a lot of damage. But you are going to have more problems if you don't brush your teeth than if you do. But you may have even more problems if you start out brushing your teeth and then stop. And so people, like we get a question all the time like, "What did people do before dental hygiene?" And the simple answer is: they had huge dental problems. But the complicated answer is: they maybe had fewer dental problems than if you brushed your teeth and then didn't ever brush your teeth again. And this is exactly what happened with polio. Which was a disease that was around and was not really at epidemic levels because people were exposed early on in their lives.

 (52:00) to (54:00)

H: And then when we got hygiene you would be exposed to polio later on in your life. And then it became a bigger problem because of the particular pathology of polio. And so you can say to that, "Well we shouldn't have done hygiene," but no. And the remarkable thing is that we've created a new problem for ourselves. And then we solved that problem for ourselves. With the polio vaccine. So it's just one big long story of trying to be a person.

D: [laughs] Yeah, you take care of one thing and then something else just comes up.

H: [overlapping] [laughing] You create another problem. But hygiene overall is good even if it led to an increase in polio that we then had to conquer in another way. Alright. Well, why don't you do Mars news and I'll try to find something about AFC Wimbledon.

D: I'll pull up the Mars news... I really liked this Mars news. It actually has a little bit of the feel of fixing the international space station with tea leaves, but just a little different. So this week in Mars news, NASA scientists and Lockheed Martin space engineers, they solved the mystery of the missing Mars orbital fuel. The Odyssey rover was built by Lockheed Martin and was launched in 2001 and it doesn't have a fuel gauge. So when scientists are tracking it they have to rely on math and various tests to figure out how much hydrazine propellant is still left from the original 500 pounds that was sent up with the orbiter. So they do this by heating up two propellant tanks to see how long it takes for them to reach a set temperature, and the emptier the tank the faster it reaches that set temperature. But recent tests in 2021 and 2022 suggested that the orbiter had less propellant than expected.

 (54:00) to (56:00)

D: And that it would be running out in less than a year, which is kind of worrisome. So the scientists from JPL and Lockheed Martin Space worked together with a spacecraft propellant estimation consultant named Boris Yendler. [laughing] Who suggested that the-- [laughs] I just really like that job. 

H: [laughing] That's great! There's one. They had a huge-- a bunch of people applied for that job.

D: [laughing] He's got the phone on ready. It's like, "This is my time." 

H: "Does anybody need any space propellant estimation? 'Cause it's all I know how to do!"

D: So Yendler suggested that the problem might be coming from some other source on the Odyssey, which might be adding heat to the fuel, which is the temperature to rise too fast during all of those fuel tank heating tests. So when they looked for it, the scientists found that there were actually heaters on the fuel line that were warming up the propellant tanks. And those were messing up the results of the tests. So taking those heaters into account, they were able to estimate that the Odyssey has nine pounds of hydrazine left, which could allow it to operate for at least a few more years.

H: That's great. Did we... Were... Should they have put a fuel gauge on it? [laughs]

D: [laughing] I don't know. I don't know if the orbiters now have a fuel gauge. I don't know how it works.

H: I don't know how you measure it. You can't do it by weight. You can't weigh it. There's no gravity.

D: Yeah, I don't know if you're just like, "Well, we've got math... Math'll help us. It'll do it."

H: "Worse comes to worst we'll call Boris."

D: Clearly they knew because they set up the infrastructure to run these tests to be able to gauge how much fuel there is.

H: [laughs] Well, in news from AFC Wimbledon... here's what I can tell you. Apparently we need to win some games before the end of the season so that we can still be in League 2.

 (56:00) to (58:00)

H: And not lose. AFC Wimbledon is now at 16th place. But I've great news: they won a game! See, what usually happens with AFC Wimbledon is that they score one goal and it's 1-0 and then the other team scores two goals. And that did happen a couple of games-- or just one game back. That is, the most recent one. But then we did a remarkable thing. Where AFC Wimbledon went up 1-0 and then they went up 2-0 and then the game ended!

D: Oh wow.

H: Yeah.

D: [laughing] Did they just call the game to an end? They were like, "We're up! This is the end! That's how it works, right?"

H: [laughs] Then the clock continued to tick until the game ended. Which is the thing that you wanna have happen. But they didn't go from 1-0 up to 2-1 down again. Which, I don't know if you've been listening, Deboki, but AFC Wimbledon has now done that more than any other team. Ever. In the history of English soccer, or some stat like that.

D: Oh man, that's wild. I'm glad that they found a way to not do that. Now they gotta just do it again.

H: And also it was a team that's higher than them in the rankings. That's what I always look at. When they win a game, I make sure-- 'cause if it's, like, the last place team I'm like, "Well, they were gonna win that game." But it was a team that's higher up.

D: [overlapping] So where is AFC Wimbledon in the rankings?

H: They're sixteenth. Of 24. And there's, like, points that they get? And AFC Wimbledon has 46 points. And if they were to be in the bottom they would need to have 36 points. So they're ten points out of relegation right now. Which is good.

D: That's good.

H: But they do have to keep winning some games. So it's good that we won a game against Walsall.

D: Walsall.

H: Yeah.

D: That's a great name.

 (58:00) to (59:19)

H: Oh, they're all great. The next two down-- so, between AFC Wimbledon and Walsall are [exaggerated pronunciation] Tranmere, which is just like-- it's exactly the same thing as Walsall for some reason? Like Tranmere and Walsall are the same. They just... 

D: [laughs] Like, they feel the same? Or they are the same?

H: They just feel the same. They feel the same to my brain.

D: [overlapping] 'Cause they have the same number of points.

H: They do have the same number of points. But to my brain Tranmere and Walwall feel--

D: [overlapping] Has anyone seen them in the same room?

H: [laughs] And then the next one, just above AFC Wimbledon is [exaggerated pronunciation] Grimsby Town. [laughs]

D: [laughing] That's great. That's amazing. I love it.

[outro music by Gunnarolla begins]

H: Alright, Deboki, thank you for making a podcast with me while John continues to recover and also I think is doing fun thing. If you wanna send us your questions you can do that at hankandjohn at gmail dot com. We don't have a podcast without your questions. Thank you very much for your science questions in particular, those are always very fun for me and Deboki to work on. This podcast is edited by Josef "Tuna" Metesh. It's produced by Rosianna Halse-Rojas. Our communications coordinator is Brooke Shotwell. Our editorial assistant, as always, is Deboki Chakravarti. The music you're hearing now and at the beginning of the podcast is by the great Gunnarolla. And they say in our hometown:

D&H: Don't Forget To Be Awesome