But that's not true.

Or at least if it was a defense mechanism, it would be a really lousy one, since urushiol doesn't bother most animals that encounter it, just us and apparently hamsters.

But it has no efffect on the animals that actually feed on the plant, like deer, insects and birds. That's why scientists think it's more likely that urushiol eveolved as an antimicrobial. It's quite effective against much smaller plant pests.

There's even been some speculation that birds that eat the seeds actually benefit from urushiol's antimicrobial and antiparasitic properties. It's simply an unfortunate accident of evolution that makes these plants in compatible with humans, so the rash, oozing blisters and relentless itching, it's all pretty much down to cosmic unfairness.

Urushiol interacts with your skin cells; specifically, ones that express a protein called CD1a. CD1 proteins help the body spot invaders and sick cells. They bind to specific fats, then show those fats to the body's immune cells.

Except human CD1a has the unfortunate tendency to set off attacks in response to things that aren't pathogenic. And it just so happens that urushiol is one of those things.

Urushiol-loaded cells activate the body's T cells, those vigilant warriors of the human immune system. Then the T cells release two proteins called interleukin 17 and interleukin 22, and they're what make you itch.

The redness, swelling and blisters all occur because your immune system harms your skin cells in its attempt to eradicate a bit of harmless oil.

Now of course, this doesn't really apply to those 10-15% who don't seem to be affected by urushiol at all. For some reason nature has seen fit to spare some people from the horrors of urushiol, but there hasn't been a lot of scientific research into why that is. It might be because urushiol-induced contact dermatitis is basically an allergy and allergies occur when the body mistakes a harmless substance for something harmful.

And like with other allergies, some people's immune systems just go haywire when encountering urushiol while others don't. It's just that most people are allergic to urushiol. But also some of the people who say they're immune probably aren't really immune.

Most people don't react to urushiol the first time they're exposed, so a person might believe they're immune when in fact they could go on to develop an allergic reaction....

... if they touch it again. And even if they've had a couple of exposure with no reaction, they could still develop a sensitivity later in life.

Increased exposure is thought to increase the likelihood of developing sensitivity, so if they roll around in a bunch of poison ivy to show off to their hyper-allergic friends, they might end up experiencing some itchy, itchy karma.

Though wierdly enough, sometimes sensitivity to urushiol fades as people get older. Scientists aren't really sure why, but it might have something to do with the fact that your immune system weakens as you get older. And a weaker immune system may not mounth as strong a defense against urushiol. So, that's one advantage to getting older.

At any rate, whether you think you're immune of not, or may have become less sensitive over time, you probably don't want to push your luck. Urushiol-induced contact dermatitis is miserable at any age, so it's always a good idea to avoid which ever version of poison whatever is in your neighbourhood.

Now, speaking of misunderstood organisms, you often hear people talk about poisonous snakes, and while that's usually wrong, it's not always.

Some species are poisonous and venomous, so double the danger. Here's Hank with more:

-[Hank] If you've ever called snakes poisonous around a herpetologist, you know that friend of yours, you know which one I mean, there's a good chance you'll receive a lecture about the difference between venoms and poisons. And it's true that most snakes aren't considered poisonous but nature loves an exception.

Meet the tiger keelback. They've got the best of both worlds: poison for their predators and venom for their prey.

It can be easy to confuse the terms venom and poison but the difference does actually matter. Both are made up of toxins, biological chemicals that mess with body functions in small amounts. The technical difference has to do with how they get into a victim's body.

Poisons enter passively, by being eaten, breathed in or absorbed through the skin. And because of that, they're usually defensive; an organism's way of saying "Hey don't touch me. You will regret that."

Venoms, on the other hand, are actively injected into the body, like via a pair of pointy snake fangs....

... for example. Venom can certainly be used defensively, but often, venomous animals are predators that use their toxins offensively, so they can enjoy a meal without all that troublesome struggle.

Sicne venoms and poisons tend to be used differently, they usually contain different kinds of toxins. So a doctor would want to treat a snake poisoning differently than a snake bite, or what's known as envenoming.

And the distinction is particularly important if the snake in question is a tiger keelback. These snakes can be found across South-Eastern Asia and they belong to a huge and diverse family of snakes called the colubridae.

These are sometimes referred to as "rear-fanged" snakes because unlike rattlesnakes or cobras which pump venom forcefully through hollow fangs in the front of their mouths, colubrid fangs sit further back in the jaw and deliver venom along open grooves. They kind of have to chew on their prey a bit to get the venom moving.

Most of the time, tiger keelbacks use their venom to take down tasty fish, tadpoles and their favourite: frogs and toads. They rarely bite humans but when they do, it's not a fantastic experience for the human.

The venom can cause hemorrhaging and mess with blood clotting, leading to excessive internal and extrenal bleeding and in several known cases, death. Thankfully antivenom is usually an effective treatment, if delivered in time.

Now all this talk of killer snake bites might sound scary but it's important to remember snake don't want to bite you. Really they don't. They'd much rather svae their venom for their prey; they don't want to waste it on something they can't eat.

And that may be partly why the tiger keelback usually fends off threats another way. on the back of these snakes' necks are several pairs of nuchal glands. I the right pressure is applied, these glands crack open and spew out a stinky, toxic, yellowish pus.

The poisonous nature of this stuff was first noted in 1935 when a scientist who was dissecting a keelback cut into its nuchal glands accidentally spraying the poison right into his eye. Which is just one of the many stories that science teachers have heard...

.. which is roughly 40 times less toxic when swallowed than when injected. But still it's a super deadly poison, so if you did somehow manage to obtain a shot glass full of venom from these golf ball-sized octopuses, you definitely wouldn't want to drink it.

I can't actually say that it would kill you because we haven't tested this venom's oral toxicity but that's kind of the thing. We haven't tested most venoms that way. There simply hasn't really been a reason to. So we don't know if they're safe to drink, though we do have some evidence to suggest that they aren't.

For instance, in a study published in 2015, rats that ingested cobra venom ended up with damage to their livers reminiscent of what happens after a regular bite. Plus, there's been at least one case where someone almost died after drinking snake win, a beverage prepared by steeping an entire venomous snake in alcohol.

And this guy wasn't suffering from run of the mill alcohol poisoning. He was admitted to the hospital because his blood had stopped clotting properly, a symptom often caused by snake venoms. And he got better after receiving anti-venom.

Researchers in Australia are actually hoping some venom toxins work orally, on insects that is, that way they can be more easily used as pesticides. And so far, 70% of the spider venoms they've tested killed the fruit flies that ate them, which sounds promising as far as pesticides go.

Now, that doesn't mean they're dangerous for us to drink but still the research is further evidence that venom toxins can do their nefarious work when ingested.

So, can you drink snake venom? I mean, maybe? It could depend on the species of snake, but we haven't done the tests to find out. And making assumptions based on the difference between venoms and poison is a terrible idea.

Yeah, we al probably should've figured that was a bad idea. But I think we can all agree that nature is amazing, and also kind of dangerous. And the science of toxins is endlessly fascinating.

If you want to dig deeper into how other toxins work, and the cool stuff they do, I am pleased to inform you there is so much more. We have episodes on poisonous house plants, and the deadliest substances on Earth, just to name a couple so...