Kids over 5 can now get a COVID vaccine in the U.S. We know a lot of you have been waiting for this day and lots of you have sent us questions about the vaccine since the pandemic started: like what's in the COVID vaccine? How does it work? How do scientists know it's safe? And even if the vaccine isn’t available to you where you live yet, this episode will answer those questions -- and there are some fun games you can play along with us!

If you have more questions about how COVID, the vaccines or anything else, you can send them to us here.

Plus we've got some tips for how to distract yourself if you're feeling nervous, and an original song designed to help you shake that arm after the shot so it doesn't get as sore. Dance those ouchies away!

Also: Three (3!) mystery sounds and a Moment of Um that answers the question: How does concrete harden?

And you can learn more about the vaccine trials for kids in this episode:

Vaccines for kids and silver linings: Our second COVID summer

Audio Transcript

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CREW: You're listening to Brains On!, where we're serious about being curious. Brains On is supported in part by a grant from the National Science Foundation.

KARA: What up, boom booms? I'm Kara.

GILLY: And I'm Gilly. We are two adorable viruses with sick dance moves.

KARA: And infectious laughter. [LAUGHS] That's right. This is--

BOTH: Going viral with Kara and Gilly!


GILLY: I am so glad you're back, Kare Bear.

KARA: Oh, Gilly boo, I missed you so much. And I missed our viralinos, too. We have the literal best listeners.

GILLY: Oh my gosh, yes, we have been swimming in fan art. The viralinos really know how to capture our fierce yet gentle demeanors.

KARA: Like, grr, but also, aw!

GILLY: Right, but-- oh, hey, wow, Kar, I just got an alert from the Flu York Times. And even more people are going to be able to get the COVID vaccines, even the-- oh man, what are they called again?

KARA: I'm going to need some more context to help here.

GILLY: They're like humans. But they're smaller.

KARA: Oh, yeah, yeah, yeah, yeah, OK, those are called dolls.

GILLY: No, no, like the ones that can move on their own.

KARA: Kittens!

GILLY: Maybe?


No, no, I'm pretty sure it's something like ch--

KARA: Chicken?

GILLY: No, ch-- ch-something? Ch-- chili-- chili dogs, chilnins, chilfonts, chiltons-- chiltons. Yep, oh yeah, yeah, that's totally it. Human chiltons are starting to get vaccines, too.

KARA: This is great news for us.

GILLY: Yes, the more humans that get vaccinated, the less we have to hear about the coronavirus.

KARA: I am so sick of her.

GILLY: Tell me about it. Also, I heard that she was thinking of starting a podcast, too.

KARA: Wow, copycat much?

GILLY: Oh, Kara, we're going to have to end the show early. The group text is blowing up after this vaccine news.


KARA: Oh dang, 44 unread messages. And wow, partiti virus finally figured out how to send GIFs. They just keep coming. That's all for today, viralinos. Oh, this one's a cat wearing sunglasses, lol. Stay infecti and don't get sanitized.



MOLLY BLOOM: You are listening to Brains On! from APM Studios. I'm Molly Bloom. And my cohost today is Gus from Seattle. Hi, Gus.

GUS: Hi, Molly.

MOLLY BLOOM: This is a special episode we've been working on for when kids under 12 can get the vaccine. And that time is here.

GUS: A COVID vaccine was approved for kids between the ages of five through 11 here in the US.

MOLLY BLOOM: And there are a few other countries where kids as young as two years old can get vaccinated, China, United Arab Emirates and Cuba. And other countries will be joining this list soon.

GUS: If you can now get the shot and you're choosing to do so, this episode is for you.

MOLLY BLOOM: We've designed it to keep you company as you get ready to get your vaccine and to keep you entertained afterwards. We know a lot of you have been waiting for this day. And lots of you have sent us questions about the vaccine since the pandemic started. Here are just a few from Arlo, [INAUDIBLE], and Xander.

CREW: My question is, how does the COVID-19 vaccine work? And what is inside of it?

CREW: How do doctors make sure the vaccine is safe?

CREW: My question is, how do vaccines work?


MOLLY BLOOM: And even if the vaccine isn't available to you where you live yet, this episode will answer those questions. And there are some fun games you can play along with us. But, Gus, you already got your shot You got it a few days ago. And you and your mom were kind enough to record how it went.

CREW: Hi, my name is Hugo. What's your name?

GUS: Gus.

CREW: Hi, nice to meet you. Do you want your shot in your left or right arm?

GUS: Oh, left.

CREW: Left? OK. Do you know what you're going to have for lunch? Have you thought about that yet?

GUS: Um, I don't know, maybe a bagel-- probably a bagel.

CREW: Do you want me to count down or not count down?

GUS: Um, no, it's OK.

CREW: No count down?

GUS: No.


CREW: Small poke.

CREW: You did great!

GUS: Oh, that was it?

CREW: That was it!

GUS: That must be a tiny needle.

CREW: It is! It's a very small needle. All right, let me fill out your vaccine card. All right, nice to meet you.

GUS: Bye!

CREW: Bye!

CREW: We're going to sit over here. How was it?

GUS: It was good.

CREW: Good, what happened?

GUS: Well, I got my shot. And it really didn't feel like much because the needle was so small. And it's not really sore either. So I thought it was pretty good.

CREW: Good job, Gus.

GUS: Thank you.

MOLLY BLOOM: Oh, Gus, that's so exciting! It was so quick. And you did not seem nervous. Nice work. I also have gotten very used to needles because I have to get allergy shots. But not everyone feels this way.

There are even adults who are scared of needles and vaccines. So whether you're feeling super confident or are a lot nervous about shots, we have a little game to pass the time while you wait. We're calling it Not Throwing Away My Shot.


Not throwing away my-- not throwing away my shot!

Every answer in this trivia game has to do with some kind of shot. Are you ready, Gus?

GUS: I'll give it a shot.

MOLLY BLOOM: OK, question one, what is it called when a basketball player attempts to make a basket from a distance while jumping straight up?

GUS: A jump shot?

MOLLY BLOOM: You're right. It's a jump shot. So fun fact, in the Guinness Book of World Records, there are over 80 records related to making basketball shots, including the most miniature basketballs shot in one minute, farthest basketball shot made with only the head, most layup shots made while juggling three basketballs, and most consecutive basketball free throw shots made by a humanoid robot.

GUS: That's a lot of records.

MOLLY BLOOM: I don't even know how you would make a layup shot while juggling three basketballs. I have trouble picturing that. It sounds very impressive.


Question two, what is it called in a movie when the screen shows two people at the same time?

GUS: A--

MOLLY BLOOM: The screen is showing two people at the same time.

GUS: Double shot?

MOLLY BLOOM: Very, very close. It's called a two shot.

GUS: Oh, that's too obvious.

MOLLY BLOOM: I know, it was too easy. There are lots of different shots in the shows and movies that we love. Wide shots, that's when you can see somebody's whole body or an extreme close up. Like, you can just see someone's eye. Back before computers, movies were shot on film, which was like a sturdy ribbon made of plastic. And in order to cut between different shots, you actually had to cut different ribbons together with razors and tape.


Question three, what is a phrase that describes when you're close enough to hear something?

GUS: Within earshot.

MOLLY BLOOM: Correct! Different sounds travel different distances. You can hear thunder from up to 25 miles away. But someone talking would be far less than that.


Question four, what is the name of the Olympic event where athletes throw heavy metal balls as far as they can?

GUS: Ooh it's--

MOLLY BLOOM: You should put your mind to thinking about how it's related to a shot.

GUS: Yeah.

MOLLY BLOOM: Put your foot on the ground. And tap those toes to help you think. You see what I'm doing here?

GUS: No.

MOLLY BLOOM: OK, I'll give you a hint. The first word of it is shot. The second word is something else.

GUS: Shot?

MOLLY BLOOM: You can put this down as a tricky one, or put your pen to paper.

GUS: Put-- shot put.


GUS: What, shot put?

MOLLY BLOOM: Yeah, it's called shot put. It's where a person stands with a heavy metal ball kind of held against their neck and their shoulder. And they spin around and then heave the ball as far as they can. That is called shot put. This kind of weight-throwing competition is thought to originate in Scotland and is over 1,000 years old. So people have been doing this for a very long time.


That's it for Not Throwing Away My Shot. Nice job, Gus.

GUS: Thank you.


Not throwing away my-- not throwing away my shot!

MOLLY BLOOM: Just like the COVID vaccines for adults, the vaccine for kids has been tested in thousands of volunteers.

GUS: The dose for the vaccine that's been approved for kids is smaller than the dose for adults.

MOLLY BLOOM: The shot that's been approved for kids in the US is an mRNA vaccine. Scientists have been studying mRNA vaccines for years. Let's revisit how they work.


The "m" in mRNA stands for messenger. MRNA is a messenger molecule that tells your cells what to do. So the vaccine contains a teeny bit of this messenger code. And this code says, make a tiny protein. And once the protein is made, this code gets destroyed, like a secret spy message or something. These mRNA vaccines tell your body to make a very specific protein, the protein that is on the coronavirus spikes.

So your body makes this protein. And your immune cells see it and are like, whoa, what is this protein doing here? Tag and destroy! Then your immune cells create antibodies against this protein and destroy it. Now, if you get infected by an actual coronavirus, your body will recognize that tiny protein and say, hey, we remember you. Get out of here!

GUS: If you weren't vaccinated, your body wouldn't be trained. So it wouldn't be ready to fight the coronavirus right away.

MOLLY BLOOM: And in the time it takes your body to realize you're infected, you get sick.

GUS: That's why vaccines are awesome. They train our bodies to fight germs so that when we do meet them, we're ready to destroy them.

MOLLY BLOOM: And just like training to run a 5K or solve a Rubik's cube quickly, this training process doesn't happen overnight. You need two doses of the vaccine about three weeks apart. And even after your second dose, your body is still learning how to fight the virus. Two weeks after that second dose, you're considered fully vaccinated. Your immune cells are fully trained.


So what's in these vaccines? And how do scientists make them? Brains On! producer Menaka Wilhelm is here to show us.

MENAKA WILHELM: Yeah, and let's start by zooming in on a vial of the vaccine. Is the zoom ray ready?

MOLLY BLOOM: I've got it all warmed up.

GUS: Yay, I love going miniature!

MOLLY BLOOM: It always makes my tummy a little wobbly.


MENAKA WILHELM: So you can see, this file is full of liquid. And in the liquid is itty-bitty vaccine mRNA. And the RNA is all wrapped in tiny fat bubbles. Those bubbles protect it in its journey into your cells.

GUS: Like bubble wrap.

MENAKA WILHELM: Precisely. The tiny, fat bubbles are like a really special version of bubble wrap. And they're protecting a pretty fragile molecule. That's the mRNA. It needs to be in tip top shape when it's time to tell your cells what to do.

MOLLY BLOOM: Anything else in there?

MENAKA WILHELM: Besides the fat bubbles and the mRNA, there's a little bit of water and a tiny bit of sugar and some special salts and acids. Sugar keeps the fat bubbles from sticking together. And then the salts and acids make sure that the vaccine blends in well when it gets into your body. Our insides are salty. Are you ready to zoom in on that mRNA itself?



All right, so the mRNA, the crown jewel of this vaccine

GUS: Wow, so this little string of molecules tells your body to make coronavirus spike proteins?

MENAKA WILHELM: Yeah, and it came from a super clean vaccine-making factory. Vaccine makers cook up this mRNA in bucket-shaped vats. And actually, it only takes a tiny bit of mRNA to make each vaccine dose. So those vats aren't necessarily that big. Some hold around 10 gallons, which is about the size of a fish tank. And a vat that size holds the recipe for many, many doses of the vaccine.

MOLLY BLOOM: I bet that's quite a recipe.

MENAKA WILHELM: Definitely, and not quite as delicious as baked Alaska, but certainly as complicated. Making a vaccine is a little bit less hands on than making a cake at home. Scientists and engineers have set up this vaccine recipe so that lots of stuff happens because of machines and molecules.

GUS: So scientists aren't stirring up batches of vaccines, one at a time?

MENAKA WILHELM: Nope, and using machines and molecules more than human hands makes things go faster. It also keeps everything cleaner. So inside those vaccine-making vats, scientists use enzymes, which are special proteins, to make the mRNA from its ingredient molecules. The raw materials for mRNA are these molecules called nucleotides.

So in one of those vats, they mix together nucleotides, enzymes, and other compounds that help the enzymes do their job. Then enzymes do the work of putting the mRNA together because that's just how those enzymes react with all of those other ingredients. It's a little bit like how when you put a cake into the oven, your cake starts out as a liquid and then over time becomes a cake, all thanks to the way that those ingredients react together.

MOLLY BLOOM: How long does it take to make that recipe of mRNA?

MENAKA WILHELM: Making the mRNA takes a little bit less than a week, which sounds really fast. But that's just one part of making the vaccine. So there's also a lot of steps to set up the mRNA recipe. And then after the mRNA is done, special mixers whip everything up so that you get those tiny fat bubbles around the mRNA.

GUS: And of course, the vaccines also have to go into their little vials.

MENAKA WILHELM: Of course! Also, a really big part of this process is double-checking mixtures and machines at different steps. So vaccine makers follow a bit of their recipe and then double check it before they move on. And the double checks often take longer than the recipe steps. But that's a good thing overall. It's super important to be sure that every part of this process is happening exactly the way that it's supposed to.

GUS: So that's why it takes a couple of months to get those batches of vaccine from start to finish?

MENAKA WILHELM: Exactly. And the batches are pretty big, like, millions of doses. Speaking of big, are you ready to zoom back out?



MENAKA WILHELM: Nothing like the zoom ray! These mRNA vaccines are pretty clever. They use a messenger molecule that our bodies know really well to teach us how to fight off the coronavirus. For each vaccine, scientists have set up a super special recipe.

They've got molecules that will react to make bits of the vaccine that they need and then machines that mix and separate and package the vaccine safely. Setting everything up to make these vaccines is definitely a big process. But people are working on it around the clock every day.

GUS: Thanks, Menaka.

MENAKA WILHELM: Nice zooming, bye!


MOLLY BLOOM: Do you have questions about the COVID vaccine, or anything else for that matter? You could always send your questions to us at

GUS: That's where we got this question.

JAN: My name is Jan. And I'm from New Mexico. My question is, how does concrete get hardened?

MOLLY BLOOM: We'll answer that question at the end of the show during our moment of Um. Plus, we'll read the most recent group of names to be added to the Brain Honor Roll.

GUS: So keep listening!


You're listening to Brains On! from APM Studios. I'm Gus.

MOLLY BLOOM: And I'm Molly. OK, so now you know how the mRNA vaccine works and how it was made.

GUS: We know it was tested in thousands of kids to make sure it's safe.

MOLLY BLOOM: If you want to hear more about those trials that made sure the vaccine is safe, you can listen to our episode called "Vaccines for Kids and Silver Linings," where we talked to a girl who participated in one of those vaccine trials. If the idea of getting that poke makes you a little nervous, here are some tips for how to handle that moment.

You can give a little cough right before the shot, cough during the shot, and one right after. [COUGH] Or you could try panting like a dog. [PANTS] Or you could try squeezing something like a foam ball. Distracting yourself is very helpful if you're feeling nervous. Brains On! producer Sanden Totten is here to share how he got through his jab.

SANDEN TOTTEN: So there I was, about to get vaccinated. My mask was bothering me a little. I had to wait for my name to be called. And I'll admit, I was just a teeny little bit nervous. But I was also hungry. And I was craving a banana, which is probably how I started to think, what if my phone was a banana?


It'd be like, ring, ring, ring! And I'd hold it up to my ear like a phone. Hello? Sorry, what was that? Oh, I'm sorry. I'm having trouble hearing you. My phone is a banana! [LAUGHS] But then I had this thought. Why am I all of a sudden in the pocket of a pants-wearing banana?


That's when I pictured a giant banana picking me up out of its pocket and using me as a phone. The banana would be like, hello? Sorry, I'm having trouble hearing you. My phone is a Sanden. Oh, that's weird. I love it. My phone is a Sanden. My phone is a Sanden. (SLOW MOTION) My phone is a Sanden.

And by the time that whole thing played out in my head, I'd already gotten my shot. And I was on my way to the fruit stand. Banana in the belly here, I come. I guess what I'm trying to say is that if you find yourself waiting to get the vaccine and you're a little nervous like me, pretending your phone is a banana or that you're a banana's phone is a pretty cool way to pass the time.

I thought I'd share in case that helps. Ring, ring, ring! OK, bye! I got to take a message for this giant banana. Hello? Uh-huh, that's appealing. OK, got to split. Bye.


GUS: Shots happened so quick. It's just a couple of seconds. And they're over.

MOLLY BLOOM: And then after, it's so cool to think about your body doing its amazing immune response we talked about earlier. Go, little cells, go!

GUS: It's that immune response that can sometimes cause your arm to hurt after a shot and why you might feel tired or achy as your body practices fighting off the COVID spike proteins.

MOLLY BLOOM: Right, you might not feel your best. But it usually passes quickly.

GUS: And fighting off the real coronavirus would most likely be way harder on your body.

MOLLY BLOOM: One thing you can do to lessen arm pain is to move it around like Gus talked about earlier. Get that blood flowing. Here with some tips on how to do that is Brains On producer Marc Sanchez.

MARC SANCHEZ: Hey, Molly. Hey, Gus. One of the best ways I know to get my arms moving is to dance. And one of the best ways to get dancing is by having a great song to sing. So I wrote this one for all of us to learn and sing and dance together. In order to do it, though, you have to stand up and get into a real fowl state of mind, fowl like bird, you know, foul? OK, are you ready to glide like an owl, flap like a chicken, rev those wings up to hummingbird speed? Well, if you said yes to any of those, then this is the song for you.


Take a step back. Now, give yourself a clap. Fly to the side for an imaginary ride. Circle round, tiny people on the ground. Lift your arms out and do that hoot owl shout. Hoot, hoot, hoot, hoot, hootie, hootie, hoot, hoot, hoot, hoot, hootie, hootie, hoot, hoot, hoot, hoot, hootie, hootie, ooh. Take a step back and give yourself two claps. Jump to the fun. Make a muscle with your arm. Put your hands in your pits. Make a cluck duck too, if time permits. Bring your elbows out and in. You look just like a chicken.


Take a step back. Now, give yourself three claps. Hey, now, have you heard? It's time to do the hummingbird. Your arms flap up and down, faster, faster whooshing sound. Find a flower or a tree Take a drink now, and go be free.






GUS: Wow, that dancing felt great!

MOLLY BLOOM: Hoo, boy, did it ever! But now, you might feel like resting. So to start off your rest time right, we have three mystery sounds for you.


CREW: Mystery sound.

MOLLY BLOOM: Gus, you ready to do some guessing?

GUS: Yeah!

MOLLY BLOOM: All right, here is the first mystery sound.


GUS: I know that sound like the back of my hand.

MOLLY BLOOM: What? What do you think?

GUS: That's rain on an umbrella, or it's rain on some sort of plastic covering, either an umbrella or one of those things that they have outside restaurants that's like, the plastic.

MOLLY BLOOM: Mm, awning. Yep.

GUS: Yeah, awning. Or maybe-- yeah, I think it's an umbrella, most likely.

MOLLY BLOOM: All right, I like it. Let's hear it again. And see if you still think that's right.


Still raining? And you're familiar with this because in Seattle, it rains a lot?

GUS: Yes, rain.

MOLLY BLOOM: I've heard that people in Seattle don't like to use umbrellas, though, is this true?

GUS: We don't, we don't. But I hear that sound a lot because some people, some crazy people do like to use umbrellas.

MOLLY BLOOM: So you just wear really good rain jackets?

GUS: Yeah, I guess, or just nothing.

MOLLY BLOOM: Like, I'm in Seattle. I get wet. That's what I do.

GUS: Yeah, if you don't like the rain, leave.

MOLLY BLOOM: All right, you ready for the answer?

GUS: Yeah.

MOLLY BLOOM: OK, here it is.

STANLEY: Hi, I'm Stanley.

AMELIA: And I'm his sister, Amelia. And that was the sound of raindrops hitting the fabric at a park.

MOLLY BLOOM: Hey, nice work!

GUS: I told you!

MOLLY BLOOM: You got it, an awning, getting hit by rain. All right, mystery sound number two, you ready?

GUS: Yeah, I'm always ready.

MOLLY BLOOM: Here it is.


It's a long one-- gave you a lot of chance to think about it, what do you Think

GUS: Maybe a washboard? Or I don't know what those sound like. It sounds like what it would look like. And it looks like what that sounds like. But that's the only thing I can think of.

MOLLY BLOOM: Well, OK, let's hear it again and see if anything else pops in your head.


What are your new thoughts?

GUS: Well, it's definitely someone doing something. It's not like a natural thing like the rain because at the beginning, I heard it going like, [GIBBERISH SOUNDS] at a consistent pace, which makes me think it's a person doing something. So I think it's a person using a washboard or something, something like that, yep.

MOLLY BLOOM: And a washboard because it sounded a little metallic, kind of?

GUS: Yeah, and it sounded rough.

MOLLY BLOOM: Let's hear the answer.

ELVI: My name is Elvi. And I'm from Portland, Oregon. And that was the sound of me crumpling tinfoil.

GUS: Oh! Oh! Yep, that makes sense.

MOLLY BLOOM: That does make sense. It makes a good noise. I really like that noise. It's almost kind of musical.

GUS: It sounded like wet tinfoil because I've made that noise before. And it sounds like wet tinfoil.


MOLLY BLOOM: All right, mystery sound number 3, and the final one.


GUS: That's it?

MOLLY BLOOM: We got to hear that again. We got to hear it again.


GUS: Sounds like something on a rack, like spoons. You know how sometimes there's measuring spoons that are lined up together on a ring? What if it's something like that, but bigger? And you bring one spoon to the top of the ring. And then you drop it. And it hits the other ones or something?

MOLLY BLOOM: Yeah, kind of like something hanging and dangling and hitting something. Let's hear it again.


Any new thoughts?

GUS: I don't know. It sounds like it's pretty likely that it's something else. But that's what it sounds the most like to me.

MOLLY BLOOM: OK, well, let's hear the answer.

WHITNEY: My name is Whitney. I'm from Madison, Wisconsin. This was the sound of a disc golf disk hitting a disc golf basket. A disc golf disk looks like a mini frisbee made out of plastic. And the disc golf basket has a poll, a top with chains hanging down from the top with a basket underneath to catch the disk.

MOLLY BLOOM: Oh, that's fun.

GUS: So it's dangling from a chain?

MOLLY BLOOM: Yeah, there's like, a pole. And then there's chains going down, connected to this basket where the frisbees go in.

GUS: Oh, so--

MOLLY BLOOM: So the frisbee hits these chains. I think their purpose is to kind of stop the disk because otherwise, it would just keep flying.

GUS: Yeah.

MOLLY BLOOM: So you kind of hit the chains. And it goes into the basket.


OK, enjoy the rest of your rest. Living through this historic time is not easy. You've had to do hard things. And we are so proud of you. And remember, we're all in this together.

GUS: Yeah, if there's one thing this pandemic has shown us, it's that it's up to all of us to keep each other safe. We're all part of the same team.

MOLLY BLOOM: Well said.


GUS: If you have any questions about the vaccine, COVID, or anything else, you can always send us your questions at

MOLLY BLOOM: We're going to be doing a special live chat with an expert to answer any questions families have about the COVID vaccine. So if you do have questions, we'd love to hear them. If you can't attend live, the video will be posted on our website and sent out in an email to our fan club members. You can join the free fan club at We're about to answer the Moment of Um question-- but first, some quick credits.

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

MOLLY BLOOM: We had production help from Tricia Babita and Dan [INAUDIBLE]. And our intern is Catherine Sundqvist. Our executive producer is Beth Pearlman. And the executives in charge of APM Studios are Lily Kim, Alex Schaffert, and Joanne Griffith. We had engineering help from Andrew Walsh and Johnny Vince Evans. Special thanks to Phyllis Fletcher, Tracey Mumford, and Anna Weggel.

GUS: Brains On! is a nonprofit public radio program.

MOLLY BLOOM: You can support the show and help us keep making new episodes at There, you can join our free fan club, donate, or check out our merch. That's

GUS: Now, before we go, it's time for our Moment of Um.


CREW: How does concrete get hardened?

MATTHEW ADAMS: So concrete is sort of like a chocolate chip cookie. I am Matthew Adams. I'm an Assistant Professor at New Jersey Institute of Technology. And I study the chemistry and durability of cement and concrete systems. With a chocolate chip cookie, you've got the flour and the eggs and the water. And you mix that together with sugar and chocolate chips.

And so in concrete, you've got sand and rocks. And those are like the sugar and the chocolate chips. And you have cement and water. And those are like the flour and eggs and water in a chocolate chip cookie. And so when you first mix all of those materials together, you have this nice pliable almost fluid-like material. And then in the chocolate chip cookie, you put it in the oven. It undergoes a chemical reaction. Everything melts together.

And you get a nice cookie that is solid and you can break. In concrete, that cement and the water undergo a chemical reaction where basically, they grow these little tendrils out from the cement grains. They get intertwined. And they lock in together. And that's how it hardens. So it takes time for that to happen. But in the end, you end up with your rocks and your sand all stuck together by this cement water matrix.

It is just an astoundingly complex mixture of chemical reactions that's happening under your feet. And those chemical reactions happen for hundreds of years. And so we can take concrete that is 150 years old and look at it under a microscope. And we can see that those chemical reactions are still happening.


MOLLY BLOOM: My love for this list of names is totally solid. It's time for the Brain's Honor Roll. These are the incredible kids who keep us going with their questions, mystery sounds, drawings, and high fives.


We'll be back soon with more answers to your questions.

GUS: Thanks for listening.

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