A pair of ghost shoes visit Molly with a message: it's time to think about garbage. They predict that Molly will be visited by three visions of garbage, one from the past, one from the present and one from the future.

Today, Producer Sanden Totten takes us on a time traveling journey to see how we started making all this trash in the first place. Plus: the Moment of Um answers the question: Are yawns contagious to animals?

Next week, we'll be back with a look at the present and future of garbage.

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KRISHA: You're listening to Brains On, where we're serious about being curious.

CHILD: Brains On is supported in part by a grant from the National Science Foundation.




GHOST SHOE 2: We said, oooh!

MOLLY: I'm awake. I'm awake.

GHOST SHOE 1: Greetings, Molly.

GHOST SHOE 2: Yes, greetings.

MOLLY: Ah! Ghosts. Wait. You're that pair of shoes I threw out last week, the ones that kept smelling like fish farts.

GHOST SHOE 1: We just had some bad bacteria in us.

GHOST SHOE 2: You could have used baking soda to stop the smell.

MOLLY: Sorry, you two. It's just you were also kind of old, and I'd gotten a new pair of red razzle-dazzle running sneakers, so.

GHOST SHOE 1: Silence.

GHOST SHOE 2: We've come with two important messages.

MOLLY: Oh, my.

GHOST SHOE 2: We've seen what happens to stuff when it's thrown out.

GHOST SHOE 1: It doesn't just disappear. It remains on Earth, waiting to break down and become one with the planet again, waiting a very long time.

GHOST SHOE 2: And some plastic things never break down. They just sit there. And they won't stop telling you about how long they've been sitting there. It's really annoying.

GHOST SHOE 1: Right? That old retainer would not stop yapping.

GHOST SHOE 2: Ugh, it's like, we get it. You're from the '80s. People hated anchovies on pizzas back then and whatever.

MOLLY: OK, but what does this have to do with me?

GHOST SHOE 1: Silence! I love doing that.

GHOST SHOE 2: You're really good at it.

GHOST SHOE 1: Thanks. Ahem, the first message is you must help deal with the problem of too much trash.

MOLLY: Me? What can I do? I'm just a girl with adorably curly hair and a plucky attitude.

GHOST SHOE 2: You must use your powers of podcasts to tell the world about what happens to trash and why we should try to throw away fewer things.

GHOST SHOE 1: To help you, you will be visited by three visions, one from the past, one from the present, and one from the future. Heed them. Hear them. Learn from them.


MOLLY: OK. What was the second message?

GHOST SHOE 1: Oh, right. Mark says it was your turn to load the dishwasher, and you forgot!

GHOST SHOE 2: We accidentally stopped at his room first. He told us to tell you that.

MOLLY: OK, I'll get right on it after I finish sleeping for the night.



Oh, it's morning. I guess it was all a dream.

MARK: Molly, you forgot to load the dishwasher, and now none of my cereal whisks are clean. You know I hate poorly mixed cereal.

MOLLY: Or was it?


You're listening to Brains On from American Public Media. I'm Molly Bloom, and my co-host today is Krisha from Shoreview Minnesota. Hi, Krisha.

KRISHA: Hey, Molly. Thanks for calling me up to do this episode on trash. Sorry to hear it was inspired by a weird dream. Those talking ghost shoes sound stressful.

MOLLY: Yeah. But I figured, hey, it never hurts to think about the waste we're making every day and what happens to it. Plus, we've gotten some great questions on this topic, like this one.

MIRABELLA: Hi, this is Mirabella.

CAMERON: And I'm Cameron.

MIRABELLA: And we were wondering, why do we have garbage? We recycle and compost but also have garbage. And we're wondering why we have garbage in general. Also, do we have any new tools or technology that will help with having less garbage in the future?

MOLLY: Epic curiosity right there. This question is so big, we decided to do two whole episodes on it.

KRISHA: Yeah, this is part 1. Part 2 will be out in a week.

MOLLY: Krisha, so I'm wondering, do you help take out the trash at home?

KRISHA: Yeah, sometimes I help carry it. And then we live in the apartment, so there's like a huge dumpster we have to carry the trash to. So sometimes I help with that.

MOLLY: So it really gives you a good idea of all the trash your whole apartment building's making.


MOLLY: Do you ever stop and think about the trash that you're taking out there or the trash that's already in there?

KRISHA: Yeah. So recently, ever since I got called here, I am very, well, you could say excited about trash. I mean, I've been trying to do a lot more recycling.

MOLLY: That's great. So what kind of stuff are you recycling more of these days?

KRISHA: Paper, plastic wrappers, stuff like that.

MOLLY: That's awesome. Are there any things that you reuse instead of just recycling or throwing away?

KRISHA: Sometimes I take toilet paper rolls and use them to make crafts.

MOLLY: Oh, that's awesome. They're very useful, those toilet paper rolls. And anything that you particularly throw-- you feel like you throw away a lot of?

KRISHA: Mostly-- you know after you have a party, there's these disposable trays, disposable spoons and stuff? Those we throw away a lot.

MOLLY: Well, today we're going to see what happens to our trash and talk about ways to make less of it, because there's a lot of garbage on the planet and it's becoming a problem.

KRISHA: Yeah. According to the World Bank, humans make over 2 billion tons of trash every year.

MOLLY: That's around the weight of 350 Great Pyramids or 5,500 Empire State Buildings.

KRISHA: Yikes.

MOLLY: And it doesn't disappear. Sure, we put it in bins, and trucks pick it up. But from there, it just goes somewhere else.

KRISHA: Some of it, like paper and banana peels, breaks down or decomposes.

MOLLY: But plastic trash doesn't break down at all. By some estimates, more than 9 pounds billion of plastic have been made since 1950. And most of it is still around.

KRISHA: Some of that plastic is recycled, but most of it isn't. It just gets buried or put in dumps, or it ends up out in nature.

MOLLY: So every year, our trash piles grow and grow while Earth stays the same size.

KRISHA: That's why we need to find ways to make less trash and use materials that are better for the planet.

MOLLY: The ghost shoes were right. We should be talking about this.

SANDEN: Molly, Krisha, I'm here to help with the episode. And I brought my new invention.

KRISHA: What is it?

SANDEN: It's a tiny projector that casts a 360-degree virtual image of the past. It makes you feel like you're time-traveling without having to leave your seat. Here, check it out.


First up, the age of zero waste.


MOLLY: Whoa, are those dinosaurs?

SANDEN: Yeah, we we're in the late Triassic. No trash here because trash is a human concept.

KRISHA: Aw, look at those cute Eoraptors-- so small and so chonky.

SANDEN: Yeah, I can project any time and turn it off with a click. I call it my Dial-an-Era Time-o-Vision Wondermatronomatic

MOLLY: Wow, super cool.

KRISHA: Molly, Sanden said it was a vision from the past, just like in your dream.

MOLLY: Whoa, you're right.

SANDEN: Now let's take a jaunt through the history of trash, shall we? First stop, the dawn of garbage. OK, here we go.


KRISHA: When are we?

SANDEN: This is several thousand years ago. You're looking at our ancient ancestors eating dinner around the fire.

KRISHA: Ooh, is that a woolly mammoth? Looks delish.


MOLLY: Oh, no, someone dropped one of those really cool clay bowls.

SANDEN: Yeah, happens all the time, even back then. We don't know a lot about the trash habits of our ancient relatives, but we do know that things like broken pottery couldn't easily be reused. So it would get left behind.

MOLLY: So it became trash?

SANDEN: Basically, yeah. The simplest answer to Mirabella and Cameron's question is that we have trash because some things we just don't know how to reuse.

KRISHA: Like broken pottery bits.

SANDEN: Exactly. But these early humans used most of the parts of the animals they killed. And they didn't make tons of stuff like we do now. Plus, most of the stuff they did make was biodegradable, meaning that over time, it broke down and became part of the environment again. So trash wasn't really a thing. We're still a pretty clean species at this point.

KRISHA: Delicious mammoth burgers and practically no trash? Sounds chill.

SANDEN: Right? Things stayed pretty low-key on the trash front for quite some time. We eventually formed settlements, and even cities. And, yeah, these had more leftover scraps, like food bits or building materials, but it wasn't much compared to today, because you see, for a long time, we had a very different relationship to our stuff.

MOLLY: What do you mean?

SANDEN: Well, let me show you. Let's head to the era of maximum usage. Now we're in Europe, the 17th century, out in the countryside. Ah, that fresh, fake virtual reality air. This is before electricity or radio or cars or microwaveable burritos. And you certainly didn't have big stores or online shopping. So if you lived far from town, like this spot here, you'd rely on folks like Pete the Peddler.


PETE THE PEDDLER: Howdy. Old Pete here with my cart of wonders. It's carrying pots, pans, thimbles, pretty lace, fabric for a dress, tea kettles, funnels, pins. Whatever you want, my cart's got it. Ain't that right, Horace?


KRISHA: Wow, Pete's cart is filled to the brim with everything.

SANDEN: Yeah, peddlers were basically walking malls. You could buy from them or trade.

MOLLY: Trade? What could a guy like that possibly need? His poor horse is already dragging half a household.


SANDEN: Well, for starters, peddlers would accept things like old metal or rubber or fabric.

PETE THE PEDDLER: Oh, you got fabric? How about this candle stick for your tatters or a shiny spoon?

SANDEN: You see, back then, almost everything was reused. I talked to Susan Strasser about that. She wrote a book called Waste and Want-- A Social History of Trash. Here's how she put it.

SUSAN STRASSER: Since most things or everything, really, at one point was made by hand, people had an idea of how much labor went into making things. And so they valued every object in a way that is really hard for us to imagine now.

SANDEN: So even worn-out items could have a second life. You'd sew patches on old clothes, turn the bones from dinner into knife handles or carve them into dominoes. And old metal or rubber you'd trade to people like Pete.

PETE THE PEDDLER: Yup. And I take your copper bits and rubber scraps and what have yous, and I sell them to the factories what made them. They melt it all down, and they make something else.

SANDEN: Even cloth had a second life.

SUSAN STRASSER: The main thing that happened with cloth was that it got made into paper. It used to be that paper was made mostly not from trees, as most paper is now, but rather from cloth. And people collected their rags. Paper factories ground them up and used them to make paper. So there were all kinds of materials that these peddlers would take in and, yes, indeed, recycle, although the word "recycle" wasn't used then yet.

KRISHA: Whoa, ye old recycling was done by Pete the Peddler?


Oh, and Horace the Horse.


SANDEN: Exactly.

PETE THE PEDDLER: You there, in the funny clothes, how much for that glowy metal thing?

SANDEN: Huh? Me? You mean my Dial-an-Era Time-o-Vision Wondermatronomatic?

PETE THE PEDDLER: Sure, it's purty. How much?

SANDEN: Not for sa--

PETE THE PEDDLER: I'll give you a jar o' jelly.

SANDEN: A jar of jelly? Sold.

KRISHA: Sanden, Pete is just a projection, and so is the jelly jar. None of this is real.

SANDEN: Oh, right. But now I'm craving jelly. Can you two wait here in the studio while I scamper off for a quick jelly and toast break?

MOLLY: Sure thing.

SANDEN: Sanden to Menaka, Sanden to Menaka. Please pre-heat the toaster to fiery furnace level. No, no, wait, make that dragon's breath. Sanden likes it extra crispy. Over.

ELECTRONIC VOICE: Brains, brains, brains on.

MOLLY: While Sanden feeds his stomach, you and I can feed our ears with a delicious--


CHILD: (WHISPERING) Mystery sound.

MOLLY: Here it is.


OK, Krisha. What do you think?

KRISHA: I feel like it's one of those things. I forgot what they're called, but they're filled with, I think, rocks and gunpowder. And when you throw them, they make a noise kind of like that. So it sounds like somebody throwing them, like multiple.

MOLLY: Oh, those little firecrackers?


MOLLY: I think that's what they're called. No?

KRISHA: I don't know. I don't--

MOLLY: Right? Those little snaps that snap on the ground?

KRISHA: Yeah, snap-its, pop-its, yeah.

MOLLY: Very good guess, and we'll be back with the answer in just a bit.


Do you have a question or a mystery sound to share or maybe a drawing of my weird shoe dream?

KRISHA: Oh, I'd love to see that. Send it to us at brainson.org/contact.

MOLLY: That's where we got this question.

ELISE: My name's Elise. I'm from Canada. And my question is, are yawns contagious to animals or just humans?

KRISHA: We'll answer that at the end of the show.

MOLLY: Plus, we'll call out the latest group to join the Brains Honor Roll.

KRISHA: So keep listening.

MOLLY: You are listening to Brains On. I'm Molly.

KRISHA: And I'm Krisha.

SANDEN: And I'm Sanden. And I just ate a six-pack of jelly toast in under two minutes. Woo. OK, where were we?

KRISHA: You were showing us the history of trash with your Dial-a-Time-o thing-a-ma-doo.

MOLLY: And we just finished up with Pete the Peddler.

SANDEN: Right, right, right, OK. So people in the countryside, they had very little trash, even in the 17th century. Things were different in cities, of course. To really show you how trash in cities worked, let's go to ground zero for garbage-- New York City. I'm dialing up the era of, hey, just get it out of here.


This is New York in the 17th century, same time as old Pete, but a different location. Still, not very modern. There's muddy streets. Buildings are only a few stories tall. People are walking to and fro. And once again, carts are super important. I spoke to another trash expert. His name is Steven Corey, and he's a historian at Columbia College, Chicago. He told me there were these people called cartmen.

STEVEN COREY: They would have cartmen. And cartmen were men that literally pushed carts.

KRISHA: Oh, I see one over there. He's pushing a giant wheelbarrow of stuff.

SANDEN: Exactly. Now big cities like this, as you can see, they did have garbage. There was animal poop on the street, old construction materials, ash.

MOLLY: Yeah, I am very glad your VR doesn't include smell vision.

SANDEN: Right? Here's where the cartmen helped out. You see, the cartmen had a guild, basically a club or a union. And Steven says their guild made a deal with the city. The city stops anyone who isn't in the guild from starting their own carting business. And in exchange, the cartmen will haul away street trash.

STEVEN COREY: So they might spend one part of the day moving things from the docks to a storage area or moving construction debris or baggage. And then they would collect garbage as well and take that to a dump.

SANDEN: And the dump back then might be a swampy area outside of town or even the ocean.

MOLLY: Oh, no! That's terrible for our fishy friends.

SANDEN: Yeah, we know that now. But back then, they saw it as a win, because all that trash would eventually fill in the watery area. And then you could pack it down, so it's new land to build on. Cities were growing fast, and they needed the space. In fact, some famous neighborhoods and cities today were once swampy dumping grounds. Let's move on.


Let's visit the war on rubbish.


KRISHA: We're still in New York City, but this looks more advanced. Now there are trolleys, and I think I see a steamship. Still no cars. And is that a factory?

SANDEN: Yeah, this is New York in the late 1800s, so about 200 years later than where we just were.

MOLLY: Wow, it's even dirtier than before. There's animal poop and food scraps and old wood along the streets. Those cartmen are not doing their jobs.

SANDEN: Yeah, so now we start to see trash really become a thing. Factories are popping up, making more stuff. People are buying more. And that means they're also throwing more away. Cleaning a city is too big a job for cartmen. So New York makes a bold hire.

GEORGE E WARING: 'Tis I, Colonel George E Waring, Junior, here to vanquish filth, terrorize trash, and put rubbish in its place. Huzzah!

KRISHA: Whoa, who's that fancy man with the handlebar mustache?

SANDEN: That is George Waring, former Civil War colonel and engineer. And he is hired to deal with New York's garbage problem. And he does it with style.


GEORGE E WARING: White Wings, the street is an abomination. Let's spic and span it for the people, yes? Huzzah!

MOLLY: Whoa, where did that army of people come from? And why are they all dressed in white?

SANDEN: Those are the White Wings. They're his army of street cleaners. He runs things like he did in his military days. But this time, the enemy is garbage. And, yeah, all those white outfits seem strange. But I spoke to Marty Melosi, a retired professor with the University of Houston. And he said there was a reason.

MARTY MELOSI: Now that seems kind of weird because of the work they were doing. Obviously, they were doing dirty work. But the whole idea was to identify these so-called "White Wings" with cleanliness, with doctors, with butchers, with dentists, with others that wore white uniforms.

MOLLY: Wow, they sure are cleaning things up. The street looks better already.

SANDEN: Under George Waring, New York was cleaner than it ever was before.

MARTY MELOSI: He even developed a juvenile street league which was made up of kids. And he gave them badges. They sang little songs. And they would roam the streets and tell people not to throw things in the streets. They actually would write up a little report, so they were kind of little policemen in some respects.


STREET CLEANER: Clean up your trash, mister!

SANDEN: Me? I don't have any trash.

STREET CLEANER: That collection of tangled metal and wires-- it's clearly garbage. Get it out of here, or I'll write you a ticket.

SANDEN: No, no, that's not trash. That's my Dial-an-Era Time-o-Vision Wondermatronomatic. It's the most amazing invention.

STREET CLEANER: The slide whistle is an amazing invention. That is trash. Get it out of here.

SANDEN: Let's go, Molly and Krisha. I need to tweak the settings on my projections so they aren't so rude. Over time, more cities started hiring special teams to really tackle the trash problem. But collecting it was one thing. Putting it somewhere it was another. A lot of cities put trash dumps near neighborhoods where people had less money or less political power, even though it was often the wealthiest people who bought the most stuff and made the most trash.

KRISHA: That sounds super unfair.

SANDEN: It is. Even when it comes to trash, we see that some people are treated differently than others. And the trash problem was about to get a lot worse. I'll tell you why right after I make these adjustments. Hold on.


MOLLY: OK, before we take any more rides through history, we've got some important business to wrap up. Let's get back to that mystery sound. Here it is one more time.


OK, Krisha, did your ears pick up anything new that time?

KRISHA: Maybe some like aluminum foil. It kind of sounded like that. Or it sounded like-- you know when you spin something to a different setting, and it makes that clicky sound?

MOLLY: So some clicking, some crinkling, something like that. You ready for the answer?


MOLLY: Here it is.

EVAN: Hello, my name is Evan, and the sound you just heard was me squashing an empty water bottle.


MOLLY: Does that sound familiar now that you know that?


MOLLY: Yeah, it's not a sound you hear every day. But when you do use those empty water bottles, they're kind of fun to play with and make some sound.

SANDEN: Yeah, that mystery sound is actually the perfect setup for our final stop.

MOLLY: So did you fix your Dial-a-Time-a-ma-jigger-oni-mo?

SANDEN: You mean the Dial-an-Era Time-o-Vision Wondermatronomatic? Why is that so hard? Anyway, yes, I totally fixed it. It's ready.


Let's dive into the era of plenty of plastic.

KRISHA: Oh, where are we now?

SANDEN: This is a suburb outside a city. The year is 1970. There are cars now; big, chunky TVs; telephones, but not cell phones. And we've suddenly got lots and lots of plastic. Can you spot any, Krisha?

KRISHA: Yeah, that girl is playing with a plastic toy. And that boy is drinking with a plastic straw. And that kiddie pool is plastic, and that woman's bracelet. And that man is eating out of a plastic bowl.

SANDEN: OK, OK, OK, OK, you got it. The point is, it's everywhere. Plastic was invented in the early 1900s. And it quickly started showing up in all kinds of products. By now, in the 1970s, it's such a part of daily life that you see it all over. But the big problem with plastics is--

WOMAN: That it's too fantastic?

SANDEN: Huh? Oh, hey, random '70s person.

WOMAN: I hope I'm not interrupting. I don't mean to harsh your scene.

SANDEN: It worked. She's much more polite than those other projections.

WOMAN: It's just I heard you talking about plastic, and I had to butt in. Gee willikers, it does everything. You can make lightweight dishes out of it. You can wrap leftovers in it. It makes groovy chairs in all colors or nifty tables. I love it.

SANDEN: Well, yeah, it does a lot, but there's a downside, too. You see--

WOMAN: Did I mention it's used in all kinds of life-changing inventions? Phones-- plastic. Nylon parachutes-- plastic. Plexiglas windows-- plastic. It's even used in life-saving medical devices like pacemakers that help the heart. It's just the most. Right?

SANDEN: Well, yeah, it really does a lot. And I guess it helped build the modern world and did a lot of good. But the problem is it doesn't go away. Plastic doesn't break down, so all the stuff you just mentioned, it'll still be here, taking up space, for generations to come.

WOMAN: Jeepers creepers, I didn't know that.

KRISHA: What about plastic recycling? Couldn't that help?

SANDEN: Yeah, a little. In the 1980s, plastic recycling started going mainstream. But we quickly learned it's a lot harder and more expensive to recycle plastic than it is to just make more. Today, only a fraction of our plastic gets reused, and most of it ends up going somewhere else with all the rest of our trash. Out of sight, out of mind.

KRISHA: And we're back in the studio.

MOLLY: Wow, that was quite a journey.

SANDEN: Whoa, it really was. And back to Cameron and Mirabella's question about why we have trash. Part of it is that we as a society decided it's OK to just throw things away instead of finding ways to fix what we have or reuse old things.

The good news is we are working on new ways to make less trash. And we're even inventing special plastics that can break down and become part of the Earth again. There's a whole Brains On episode all about plastics that talks about some of this stuff, so feel free to go check that out.

MOLLY: We'll also have more on how we can tackle our trash problem in our next episode.

KRISHA: Thanks for stopping by and showing us all this history, Sanden. Your new invention with the very long name is awesome.

SANDEN: You mean the Dial-an-Era Time-o-Vision Wondermatronomatic. Yeah, I really should rename it. It was my pleasure. And the idea for this whole thing came to me after this scary dream I had.


MOLLY: Wait, you had a scary trash dream? I think I had the same scary dream, where they're talking shoes.

SANDEN: What? Talking shoes? No, no, my scary dream was that you did an episode, and I wasn't in it. Could you imagine what my fans would think?


Speaking of which, I better go post some more selfies for the Sand Squad. Oh, and I think I should share my jelly toast recipe. The key is letting the bread turn black in the toaster. OK, later.


MOLLY: Bye, Sanden.

MEN: (SINGING) Ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, Brains On.

KRISHA: Molly, wasn't that weird how you had a dream that said you'd see a vision from the past, and then you saw a vision from the past?

MOLLY: So weird, but probably just a coincidence. I mean, it's just-- yeah.


Did you hear that?

KRISHA: Hear what?

NARRATOR: Meanwhile, in the Brains On headquarters kitchen.

MARK: Smells like something burned in here. Oh, well, time to eat my mixed cereal.



What was that?


GHOST SHOE 2: It's us.

MARK: Oh, those flying ghost shoes from last night. Did you tell Molly she forgot about the dishes?

GHOST SHOE 1: Yeah, we totally did.

GHOST SHOE 2: Can we have some of your cereal?

MARK: Aren't you ghosts? And also, aren't you shoes? Do ghosts and shoes even eat cereal?

GHOST SHOE 1: Only one way to find out.

GHOST SHOE 2: Pour us a bowl.

MARK: All right, here you go.




NARRATOR: Will Molly be visited by two more visions? Will she and Krisha finish telling the world about garbage? Will the ghost shoes be able to eat the cereal, or is it just falling through them onto the floor?


It's definitely falling through them onto the floor. What a mess! Anyway, tune in next week for the thrilling conclusion to this look at the past, present, and future of trash. See you then.


KRISHA: Humans have left behind things for thousands of years. But as their societies grew, so did our trash.

MOLLY: For a long time, we reused most of the stuff we had. And the stuff we couldn't reuse was dumped away from settlements.

KRISHA: But over time, we made more and more garbage, and the invention of plastic made it worse.

MOLLY: That's it for this episode of Brains On.

KRISHA: Brains On is produced by Sanden Totten, Menaka Wilhelm, Ruby Guthrie, Mark Sanchez, and Molly Bloom.

MOLLY: We had engineering help from Eric Romani. Special thanks to Eric Wrangham, Stuart Bloom, Lulu Doucette, Vicky Krekeler and Rosie DuPont. And we want to give a shout-out to Kristina Lopez, our dear friend, who is moving on to an awesome new gig. And we will miss her so much.

KRISHA: Before we go, it's time for the Moment of Um.


ELISE: Are yawns contagious to animals, or just humans?

ZOE ROSSMAN: That is an awesome question. And the answer is, yes, there are animals that yawns are contagious in. Hi, I'm Zoe Rossman. I am a scientist who studies animal behavior. And specifically, I studied whether elephants yawn.

A yawn that is spontaneous might be you wake up in the morning, and one of the ways that you help wake yourself up is by yawning. And the difference between that and contagious yawning is contagious yawning doesn't happen without somebody else yawning. As of now, we know that baboons and chimpanzees and wolves and sheep and budgies and elephants will all yawn to other animals. And some animals, like dogs and chimpanzees, will actually yawn in response to humans.

And it's really interesting, because when we think about just spontaneous yawning, that's really, really common. Fish do it. Some turtles do it. Birds do it. Mammals do it. But contagious yawning has only been seen in a few really highly social animals. We wanted to look at, one, whether elephants yawned in response to other elephants yawning, and also whether elephants yawned in response to people they knew yawning.

And so we used nighttime video cameras that were set up in an enclosure where the elephants slept. And we reviewed hundreds and hundreds and hundreds of hours, looking for yawns. We had seven elephants that we were using in this experiment, and three of them actually yawned contagiously in response to people that they knew yawning at them. And we really think contagious yawning has some sort of social implications, even though we don't really know what those are.

But there are animals like hippos, that yawning is a sign of aggression. So they'll do these really big yawns to show other hippos who's boss. And so there definitely are other types of yawns and other ways that yawns are classified that aren't just the types of yawns that you and I would do.


MOLLY: I am wide awake and ready to read this list of names. It's time for the Brains Honor Roll. These are the incredible kids who share their questions, ideas, mystery sounds, drawings, and high-fives with us.



ELECTRONIC VOICE: (SINGING) Brains are all alive.

MOLLY: We'll be back next week with part 2 in this series on garbage.

KRISHA: Thanks for listening.

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