[ intro ] [Squeaks is reading to Jessi from a joke book.] I don’t know, Squeaks.

Why didn’t the potato cross the road? [Squeaks tells her.] Ohhh, because it’s a potato, and it doesn’t have any legs! [She laughs heartily.] Oh, it feels good to laugh. We laugh pretty much every day.

But what is laughing, anyway? Why do we make this weird noise when we're happy or think something is funny? Scientists have found that we use laughter as a form of communication, which means talking and sending messages to each other.

When we laugh, we’re communicating with to the world around us! It helps us connect to other people, and strengthens our relationships. And even though we usually laugh without even thinking about it, it's actually a kind of complicated thing for our bodies to do!

When you laugh, your body uses fifteen different facial muscles, and your upper lip gets turned up. Your windpipe, which you use to breathe, is partly covered up, which makes you gasp. Sometimes, when you’re laughing really hard, it becomes harder to breathe, so you turn red or purple, and you might even get tears on your face, too.

They're happy tears! Meanwhile, your brain gets excited, and so do your arms, legs, and stomach muscles. And of course, when you laugh, you make a sound.

There's a lot going on! All kinds of situations can make us laugh. Sometimes it might be silly things that don’t go together – like putting a hat on a hamster – or sometimes it might be relief because something that made us stressed or worried is over.

Sometimes laughing can tell the people around us that we feel safe and happy with them. Or it might even be a response to being tickled! And even though funny things make us laugh, most of the time when we laugh it's for a different reason.

Usually, we’re the ones laughing at our own words. So I’m a lot more likely to laugh after something not-too-funny, like, “Squeaks and I went exploring today!” than if Squeaks tells me a joke. [Squeaks protests.] Not that I don’t like your jokes, Squeaks. It’s nothing personal.

It’s science! And even though laughter feels like the sort of thing that happens suddenly and unexpectedly, it turns out that most laughter happens during natural breaks in our conversation. People don’t usually laugh when they’re alone.

But when you're with friends, laughter can be contagious! When people say something is contagious, or catching, they're usually talking about germs, like how everyone in your class seems to get each other sick at the same time. You don’t laugh because of germs, of course, but if your friend starts laughing, you can catch their laughter.

It helps you tell the people around you that you feel comfortable, and want to be part of the group. So one person laughing can sometimes mean that a whole bunch of people will start laughing. Some scientists think that a looooong time ago, ancient humans developed the ability to laugh even before they started using words.

Even then, laughing would have helped to show that we feel safe and comfortable, and helped connect people to each other. Making connections with people, and forming groups, can sometimes mean that some people get included in a group, while some people feel left out – which may explain why a group of people being mean to someone can feel funny at first. Sometimes people might feel like they want to laugh at something bad happening to somebody.

But even though it can feel like you're not laughing on purpose, we always try to be careful about how we treat people. Laughing feels great when you're using it nicely! Laughing to connect with other people is a very human activity, but some other animals do it too!

Apes have an open-mouthed “play” face, and they make a panting sound that’s similar to the “ha-ha”s we make when we laugh. Even rats do something that's kind of like laughing! [Squeaks laughingly asks: what about robot rats?] Yes, even robot rats! Babies who haven’t learned to use words yet can laugh too.

And babies and apes laugh at similar things – like playing and tickling. Ever heard someone say that “laughter is the best medicine”? That’s because the best part about laughing is not just that it feels good… it’s good for you!

People who laugh a lot are more likely to have healthy hearts, and they tend not to get sick as much. Laughing also probably means you’re living a fun life, and have connections with people you like – and that’s healthy, too. Any of those sound like a great reason to have a good laugh! [Squeaks tells Jessi another joke].

I don’t know, Squeaks; what fruit /do/ sheep like best? [Squeaks tells her.] Baaaaaaa-nanas? Oh, that’s your best one yet! Hee hee hee! [Jessi and Squeaks dissolve into giggles.

Jessi says the outro through laughter.] Thanks for joining us! If you have questions about laughing, or jokes you want to send us, we'd love to hear them! Just grab a grown-up and send us a message at patreon.com/scishowkids.

We'll see you next time here at the fort! [ outro ].