Ink is amazing. It helps us captures our thoughts, comes in many colors and some of it is even made by animals! In this episode we explore the history of this special substance. We’ll also talk squid ink with biologist Sarah McAnulty and explain how tattoos work.

Plus, your poems about ink! Obviously there’s also a Mystery Sound and a Moment of Um that answers the question: what happens if salt is poured on snails?

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SPEAKER 1: You're listening to Brains On.

SPEAKER 2: Where we're serious about being curious.

SPEAKER 3: Brains On is supported in part by a grant from the National Science Foundation.



SPEAKER 4: Hello, and welcome, everyone. Welcome to Ink Outside The Box. We are a showcase of talented poets inspired by the greatest inkers of our time.


But first, everybody, let's see what kinds of ink appreciators we have here tonight. Round of applause if you're a clicky pen.


And how about markers? Any markers out there? Don't be shy. I know you all tend to show up in packs of 12.


Any quill pens make it here tonight? Quill pens?


Perfect. We are so glad to have you all here. And now, on with the show.


We have got a great batch of poems for you. Let's get started with a few limericks. [LAUGHS] Or should I say limerinks.


Our first limercist, Kaavia from Atlanta, Georgia

KAAVIA: Ink is smelly, it's not supposed to go in your belly. You use it to write, and day or night, it's used by Kelly.


SPEAKER 4: We all love the Kellys of the world, am I right?


OK. Our next limerick is by Tilly from Los Osos, California.


TILLY: There once was a jar full of ink. It was not purple, it was pink. It fell on the floor and started to pour, and that was the end of the ink.



SPEAKER 4: OK. Our next poet is Gracie from Adelaide, Australia. I think she'll remind us of ink's limitless potential.


GRACIE: Ink flows from the pen in all different colors, from dark red to bright blue. Handwritten or printed. Read as a poem, a book, or a rhyme. But the ink knows, it knows very well that it stains the page as a curve or a line, and it's taken into whoever's mind as a word.


SPEAKER 4: Oh, such beautiful prose, Gracie. Now, we'll let those terrific verses [CLEARS THROAT] dry on the page.


Let's take a moment to stand up and stretch. You can all adjust your caps and check out the refreshments in the lobby. We'll take a quick break. An inktermission, if you will, and join you again shortly. Ta-ta.


MOLLY BLOOM: You're listening to Brains On from American Public Media. I'm Molly Bloom, and I'm here today with two co-hosts, Tobias and Mattia from Lymington, Ontario in Canada Hi, guys

MATTIA: Hi Molly

TOBIAS: It's good to be here.

MOLLY BLOOM: Well, thank you for being here. We're really excited to have you here today. And we're especially excited because we are here to talk about ink. The stuff that goes into feather quill pens, markers, and tattoos, and also, the kind that comes out of sea creatures.

TOBIAS: It's going to be incredible.

MATTIA: I think quill have a great time.

MOLLY BLOOM: Definitely. You cant spell think without ink. And we've been asking our listeners to think about this wonderful stuff. So, Tobias and Mattia, you two sent us an ink poem, and a little skit about ink. And it seems like you did some research to write them. So I want to ask, what do you first think about when you think about ink? And, Tobias, let's start with you.

TOBIAS: Well, how much we unconsciously use it. Because it's in our printers, it's in our pens, it's everywhere. And, well, I often think about ink as this old-fashioned stuff they dipped quills in. But it's still around very much.

MOLLY BLOOM: Yeah. And what about you, Mattia, what do you think about when you think about ink?

MATTIA: I think about pens, really.

MOLLY BLOOM: And do you have a favorite ink fact that you learned while you were writing your skit?

MATTIA: I really liked learning that research has been done to see if squid ink can treat cancer. And so far, the results are hopeful.

MOLLY BLOOM: That's really cool. Yeah, squid ink is amazing, and we're going to talk about that in just a little bit. And, Mattia, I want to ask you, do you have a favorite writing utensil?

MATTIA: Marker. When we go to bed, I have coloring books, and I have a box of markers, so I always color in that to calm myself down.

MOLLY BLOOM: Oh, that's really cool. And what about you, Tobias, what's your favorite ink writing utensil?

TOBIAS: A pen. I always draw in black and white, so I'm not into the markers.

MOLLY BLOOM: So a really good black pen will set you up right?


AUTOMATED VOICE: Brains, Brains, Brains On.

MOLLY BLOOM: Now, let's talk a little bit about the history of ink.

MATTIA: Yeah. There's actually a company that specializes in historical ink products.

TOBIAS: Well, the company is imaginary, but their infomercial is good.


INDIGO: Hello, I'm Indigo Blotsworth, and I'm joined by my good friend Mr. Graphy.

CALLI: Oh, Mr. Graphy is so formal. You can call me Calli. Calli Graphy Why are we here again?

INDIGO: We're selling this box of pens featuring some of the most famous writing instruments of all time.

CALLI: Oh, right. I still don't get it.

INDIGO: Just follow my lead. [CLEARS THROAT] Pens. They're how we communicate our ideas, observations, and artwork. But have you ever wondered about how it all got started. Us, too. Now you can experience pens through the ages with the new historical pens box.


Order now and you'll get four. That's right, four different historical pens.


Each box comes with two bottles of ink. This is lamp black, one of the earliest inks ever made. It takes soot from oil lamps, that black powdery stuff that's left after you burn something, and mixes it with glue or gum.

CALLI: Lamp black. Ah. Because it comes from oil lamps, and it's black. So straightforward.

INDIGO: In ancient China, they took the lamp black to the next level by mixing it with more glue and charred animal bones. They called this--

CALLI: Gluey bone ink.

INDIGO: No. It's called India ink. Because they got most of the materials from India.

CALLI: I liked gluey bone ink better, though.

INDIGO: OK, now on to the pens. Let's start with the reed pen, straight from ancient Egypt.


The Egyptians use these long blades of grass called reeds to dip into ink and write.

CALLI: So organic, so innovative. And hey, they made great drumsticks.


INDIGO: All right, enough of that. Let's move on to the MVP.

CALLI: Most Valuable Pen.

INDIGO: Precisely. It's the fabulous feather you didn't know you needed. The quill.


CALLI: This quill is a thrill. I feel so fancy. Bring me my tea and crumpets, please. I need sustenance when I write a love sonnet with this elegant quill pen.

INDIGO: Just like the reed pen, you dip the quill into the ink and write. The quill dominated the pen game from its invention in the 6th century, all the way to the 19th century. It's what they used to write the American Constitution.

CALLI: The forefathers must have been so exhausted with all of this dipping. Imagine the wrist strain. My hand is already tired, I've only written two words.

INDIGO: You wrote stinky and butt.


INDIGO: I thought you were writing a sonnet about-- never mind. But you are right, the problem puzzled pen lovers for centuries. How do we move beyond dip pens? The answer, the fountain pen.


CALLI: Woo, now, this is a classy pen.

INDIGO: Sophisticated and revolutionary. Fountain pens put ink inside the pen itself. They used reservoirs, these skinny tubes filled with ink that go inside the pen. This means no more dipping. The ink flows down from the reservoir to the nib, the sharp tip of the pen.

CALLI: You mean this pointy thing?



INDIGO: Yes. The fountain pen isn't perfect.

CALLI: I'll say. It's taking forever to dry. I've got smudges all over the place.

INDIGO: Well, here's where the latest and greatest in pen technology comes in. The ballpoint.


It's still the most popular pen today. If you look closely, you can see there's a small ball at the tip of the pen.

CALLI: So awesome. And if you grab two of them, they work as chopsticks. See?


INDIGO: Where did you get that sushi?

CALLI: From my pocket.

INDIGO: It's covered in lint.

CALLI: You mean pocket seasoning. Mm, inkalicious. [SWALLOWS]

INDIGO: Right. Anyway, a journalist invented the ballpoint pen in the 1930s. He was experimenting with quick-drying newspaper ink. The ink was too thick for his fountain pen, but he discovered that when he put a ball at the tip, it stopped the pen from drying up, and it helped distribute the ink more evenly.

CALLI: It's so magnificent. I could look at this adorable little ballpoint all day.

INDIGO: That's right. Call now and we'll throw in a set of magic markers.

CALLI: Ooh, are these the scented kind? Grape is my favorite. [INHALES] [EXHALES]

INDIGO: Markers are the new kids on the block. They weren't invented until the 1940s and 1950s. They have two reservoirs of ink, and tips originally made of wool felt. It soaks up the ink and allows for all different kinds of marking. Perfect for coloring and making posters. What do you think Calli?


Calli? Calli? Calli?


INDIGO: Calli?

CALLI: Now I smell like a grape.

INDIGO: Calli, your entire neck is purple.

CALLI: Well, I thought these scented markers could also double as perfume. Now I'm the innovator.

INDIGO: We do not recommend the use of markers on your skin. Come now, and start your own incredible journey.

CALLI: Pens, they're penrific!

INDIGO: We said we weren't going to use that tagline.

CALLI: Pens, oh, pen the door to a brand new world. Pens, full of ink, but not one stink. Pens, perfect pens promote pretty positive ponderings. Right on. That's right with a W.

MAN AND WOMAN: (SINGING) Ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, Brains On.

MOLLY BLOOM: And now, something I bet you'll have an inkling about. It's the--


WHISPERING VOICE: Mystery sound.

MOLLY BLOOM: Here it is.


All right. What is your guess? Let's start with you, Mattia. What is your guess?

MATTIA: Well, it sounded sort of like a plastic bucket. Maybe filled with rocks, and it's somehow sticking to the pail, and you're scraping it out.

MOLLY BLOOM: Very good guess. What about you, Tobias, what do you think it might be?

TOBIAS: I thought it was maybe someone digging in a bag of lentils. Or-- yeah, or maybe rice or corn. Like, dry corn, maybe? I don't know.

MOLLY BLOOM: Well, very good guess. We're going to give you another chance to hear it and take another guess a little bit later in the show.


MOLLY BLOOM: Now, there's also a kind of naturally occurring ink. And naturally, many of our listeners are curious about it.

MAUREEN: Hello, my name is Maureen, and I am eight years old.

GABRIELLE: I am Gabrielle, and I am 10 years old.

MAUREEN: We are from Caracas, Venezuela. Our question--

GABRIELLE: Is, how do octopuses make ink?

ISABELLA: My name is Isabella.

MATTHEW: My name is Matthew.

ISABELLA AND MATTHEW: And we're from Christoval, Texas. Our question is, is octopus ink the same ink that is in pens?

TANA: My name is Tana, and I am from Thailand. My question is, how does an octopus produce ink?

TOBIAS: We talked with squid expert Sarah MacAnulty to find the answers.

MOLLY BLOOM: She told us, squids and other cephalopods make ink in their ink sacs. It's not the same ink that's in our markers and pens, it is made of pigment though, and it's very, very useful to these squids.

SARAH MACANULTY: It's made out of pigment, and sometimes mucus, sometimes not. So it depends on basically what the squid wants to do would the ink.


There are a couple of things you can do with ink, depending on the situation that you're in. So let's say you just want to create a big smoke cloud, and escape in the smoke cloud. Then you pretty much shoot out just pigment. The one other cool thing about ink is that, when one squid or cuttlefish inks, the other squid or cuttlefish in the area, and octopus for that matter, can taste "I'm nervous" chemicals in the water, and they're like, oh, something's up. One of my friends is nervous, so maybe I should be on alert.


Sometimes, there are some cephalopods that do something a little different. And so we call those pseudo morphs, which is like a fake blob, a blob of ink that is about the same size and shape, roughly, as the squid. So what they do. They mix mucus in with the pigment, and then they leave that blob of ink where they just were. So they squirt out this little blob while they're swimming backwards really quickly. And so they leave a little black blob where they used to be, in the hopes that the predator then attacks the ink blob instead of them. And so that's pretty successful and really cool.

And then the third thing that some do-- and this is just only one that I know of does this. This is the pygmy squid. They live around Australia in the Indo-Pacific, and they're like teeny, teeny, tiny. They're like the size of maybe your pointer finger fingernail length, but even skinnier. The width of maybe a pencil lead, and the length of your pointer fingernail. They're so little. They're the smallest cephalopods.

They are really sneaky, they eat really tiny shrimp. And so when they're trying to sneak up on the shrimp, they'll shoot out a little blob of ink, again, one of the ones that are kind of held together with the mucus, and they'll hide behind that ink like a hunting blind. And then when they see that the shrimp is sort of doing its thing, not really paying attention, they'll swim through the ink and pounce on the shrimp. You can also just use ink to put something distasteful in your predator's mouth so that they don't really want to pursue you anymore. Yeah, that's basically the range of things you can do.

MOLLY BLOOM: Sarah is also the executive director of Skype a Scientist. She and a lot of other very smart scientists have volunteered to Skype with families in classrooms to answer their questions on a huge range of topics. Are you curious about squids or octopuses? You could Skype with a scientist like Sarah.

Itching to know more about black holes? There's a scientist there who can answer your questions. Do you have questions about brains, or archaeology, or insects? If there's a topic you're interested in, they probably have a scientist with answers to your questions. It's totally free, and you can check it out at




SPEAKER 4: Welcome back to Ink Outside The Box. The only show that highlights highlighters. Hey! I hope everyone got the refills they needed at concessions. I'm looking at you, printer cartridges. I know you have very specific tastes.



All right, all right, let's continue with the poetry. And now, let's hear from Moira. She brought this poem all the way from Virginia.


MOIRA: Ink in pens and things, there are different types of ink. Ink in markers, too.



SPEAKER 4: Wow. That one makes me th-ink. [LAUGHS]


And now we have a special brother and sister performance. Oscar and Matilda will perform their ink poem.

OSCAR: With me playing my baritone ukulele, and my sister singing, credit to Beethoven.

SPEAKER 4: Oh, how clever. The rhyme is set to Beethoven's Ode To Joy. Take it away, Oscar and Matilda.

MATILDA: Inky, inky, we adore thee, shoots out of a ballpoint pen. Inky, inky, we adore thee, also in [INAUDIBLE], my friend.


OSCAR: Thank you.

SPEAKER 4: Oh, so true. Our octopus friends do squirt ink. Brilliant! I hope you've enjoyed all these poems, ink appreciators.


SPEAKER 4: Wait, what's that?


SPEAKER 4: A standing ovation? An encore, you say?


SPEAKER 4: You've got it. We'll be back in just a few with another round of poems. In the meantime, please take advantage of the all-you-can-ink fills at the snack bar.



MOLLY BLOOM: It is so cool to hear all the great ink poems you wrote us, and now we want to hear from you about colors. If you invented a superhero based on a color, what color would you choose? What name would your superhero have? What is their superpower? So, Mattia, Tobias, do you have any ideas about your color superhero?

TOBIAS: Ferocious Fluid. The Blue Soo. He can take the form of literally anything, like a fluid. And the only thing he fears is fear itself and particle accelerators. He likes his liquid form.

MOLLY BLOOM: [LAUGHS] That's awesome. I love that. Mattia, do you have a superhero you came up with?

MATTIA: Yeah. I chose the color gold. And my superhero is called Golden Star. She can run across the stars, has long, flowing golden hair, which is why she's called Golden Star. She spreads joy to the joyless, peace where there is war, love to the ones who feel only hatred, and hope to those who have lost all hope.

MOLLY BLOOM: Wow. That is beautiful. Wow, really nice work, both of you. Well, listeners, tell us about your color superhero ideas at

TOBIAS: Maybe you know exactly what your superhero looks like. Send us a drawing.

MATTIA: Or if you'd rather send in a quick description, record yourself and send it to us.

MOLLY BLOOM: That's how we got this listener question.

ANGELA: Hi, my name is Angela from Rockville, Maryland. My question is, what happens to snails when you put salt on them, and why?

MATTIA: The answer to that question is coming up at the end of the show.

TOBIAS: In the Moment of Um.

MOLLY BLOOM: And we'll read the latest group of listeners to be added to the Brain's honor roll.

TOBIAS AND MATTIA: Keep listening.

MOLLY BLOOM: You're listening to Brains On from American Public Media. I'm Molly.

TOBIAS: I'm Tobias.

MATTIA: And I'm Mattia.

MOLLY BLOOM: Time to tackle some more ink inquiries. Here's one about a special kind of ink.

MATTIA: The kind that goes under your skin.

TOBIAS: We're talking about tattoos.

JONATHAN: Hi, my name is Jonathan. I am from Sydney, Australia. I was curious. How do tattoos get attached to you?

PAULINA VELASCO: I can help with that.

MOLLY BLOOM: Hey, reporter Paulina Velasco. Welcome.

PAULINA VELASCO: Hey, Molly. Hey, Tobias and Mattia. You know, I've actually had tattoos on my brain lately. I mean, I didn't get tattoos on my brain. That would be weird, because no one would see them. But I've been looking into the history of tattoos.

TOBIAS: Cool. What did you learn?

PAULINA VELASCO: Well, let's start with the basics. You know how you get a tattoo?



Just kidding, it's not that scary. But it is a little painful. What happens is, a tattoo needle punctures your skin. It makes a tiny wound.


PAULINA VELASCO: I know. And at the same time, as it pierces your skin, it inserts a drop of tattoo ink right under the outermost layer of your skin, your epidermis.


And this is how it stays in there. Tobias, Mattia, have you ever scraped your knee?

TOBIAS: Is there a kid out there who hasn't scraped their knees?

PAULINA VELASCO: [LAUGHS] Really good question. So you know how sometimes, you get little bits of dirt and stones that get stuck in your scrape?

TOBIAS: Well, yeah. Often, when you scrape your knee, you scrape it. And there's often gravel, unlike the pavement or whatever.

PAULINA VELASCO: Well, it's the same with tattooing. Usually, when you get hurt, your body sends a kind of cell called a macrophage to your injury.


SPEAKER 5: OK, macrophages, we got a knee scrape here. You know what to do. Eat up the little bits, clean up the wound, yada, yada, yada.

PAULINA VELASCO: The macrophages swallow up the bits of dirt and damage cells in your wound to help your body heal.

BOSS: Maxwell, destroy that dirt. Matilda, gobble that grit. Marty, bag up that busted cell. Everyone. Oh, you're doing A-plus work. All right. We'll have this knee good as new in no time.

PAULINA VELASCO: But the tattoo ink is made of particles that are too big for your macrophages to break down.

SPEAKER 5: Boss, minor problem here. I ate this giant ink particle, and [CLEARS THROAT] now I can't quite seem to digest it. I'm not sure what to do with it. Any thoughts?

BOSS: Hmm. Yeah, we'll try to figure out something. But in the meantime, why don't you just stay put?

SPEAKER 5: Okey dokey. Staying put with this ink particle for the foreseeable future. I'm too full to move, anyway. Yeesh.

PAULINA VELASCO: Your body closes up the wound, but the ink stays right under the surface of your skin, leaving the tattoo design.

MATTIA: So what kind of ink do tattoos use? Is it like pen ink?

PAULINA VELASCO: Yeah. A lot of pens use things called pigments to give the ink color. Tattoos also use pigment. But tattoos have been around for so long, that there have been all kinds of recipes. The pigment that's used is usually in powder form, and it's made into a liquid by using a carrier like water or alcohol.

So some of the earliest tattoo ink was made from charcoal or ash. That dark soot that piles up after a campfire. One of the oldest ink recipes we have was recorded by a doctor in ancient Rome.

AETIUS: Recipe for tattoo ink, by Aetius of Rome. Combine powdered pine bark from the finest pine, preferably Egyptian. Mix together corroded bronze, the rustier the better, with vinegar. Combine with vitriol and soak, in one part, leek juice, two parts water. And don't forget, a pinch of gar. Preferably made by insect eggs, of course.

TOBIAS: Eww. Insect eggs?

PAULINA VELASCO: Yeah. But different cultures use different recipes. See, the fascinating thing about tattoos is they appear in cultures around the world. And they mean different things to different groups.


You've got the Tahitians, and Maori, and other Polynesians from the South Pacific, who have really cool geometric patterns. Like swirls that look like ocean waves. There are mummies that show us how people tattooed themselves in ancient Egypt. On their bellies and thighs, with a picture of the god that protects you in childbirth.

In the Nazca culture of South America, they tattooed their hands and fingers. In the Scythian civilization that lived in Eurasia, the more tattoos you had, the more important you were. They had elaborate tattoos of panthers, and sheep, and mythical creatures. The Japanese also have elaborate designs of dragons. Inuit women up in the Arctic tattoo elegant stripes on their cheekbones. And Berber women in Algeria have fine dots on their faces.

TOBIAS: Wow, I see what you mean. Tattoos are a global thing. So who started it all?

PAULINA VELASCO: Well, the word tattoo comes from Tahiti. When the Europeans first landed on the Tahitian islands in the Pacific Ocean in the 1700s, they heard the Tahitians, who were covered in ink, use a similar word. And they brought the word and the practice back home with them.

But the first known tattoo, that's much older than the word itself. In fact, one of the oldest mummies ever found has tattoos. He's over 5,000 years old. We don't know what he was called, so scientists named him Otzi the Iceman. Hi, Otzi.

OTZI: Hello.

TOBIAS: Oh, wow. Where'd you come from, Otzi?

OTZI: Well, good question. I am told that I was found in a glacier frozen solid, in a range of mountains that I think are-- what are they called?

PAULINA VELASCO: We call them the Swiss Alps. Or the Otzal Alps.

OTZI: After me?

PAULINA VELASCO: Well, more like your name came from them, but sure.

OTZI: Well, I obviously don't remember much, seeing that I was frozen in a glacier for 5,000 years.

MATTIA: Wow. And you have tattoos?

OTZI: That's a funny word. Tattoo. [LAUGHS] What are you referring to?

PAULINA VELASCO: They mean the parallel blue lines you've got on your skin, Otzi.

OTZI: Oh they're called tattoos now? Man, I've missed so much. Are yak pelt still cool? Anyway, yeah, I've got them on my lower back, my left knee, my left calf, and my right foot and ankle. They're little short lines of ink.

PAULINA VELASCO: Scientists think they were therapeutic, and possibly made to help with pain. Kind of like acupuncture. He was a herder and probably had achy joints.

OTZI: Much good they did me. I ended up stuck in a frozen mountainside anyway. Harrumph.

PAULINA VELASCO: Sorry about that, Otzi. We'll let you go back to resting.

OTZI: See ya.

PAULINA VELASCO: So tattoos have been around a really long time. But only recently, have we gotten any good at removing them.

MATTIA: You can remove tattoos?

TOBIAS: I thought the whole idea was that they were permanent.

PAULINA VELASCO: So remember how tattoos work in the first place?

TOBIAS: The pigment particles in the tattoo ink are so big, your body can't break them down, so they stay in your skin.

PAULINA VELASCO: Yes, exactly. So nowadays, you can use a laser to zap the pigment and break those particles down. And that makes it so that your macrophages can swallow them up bit by bit.


LAZER: Now, this I can gobble. [GOBBLING]

PAULINA VELASCO: It's slow and expensive, and can also be kind of painful. But, hey, eventually, the tattoo ink disappears.

MOLLY BLOOM: Wow. Thanks for all this info, Paulina. I see why you've been so interested in tattoos.

TOBIAS: Yeah, there's a lot to learn.

PAULINA VELASCO: For sure. Well, my job here is done. Until next time.

MATTIA: Later, Paulina.


MAN AND WOMAN: (SINGING) Ba, ba ba, ba, ba, ba, ba, ba, ba, ba, Brains On.

MOLLY BLOOM: All right. Let's get back to the mystery sound. You guys ready to hear it again?


MOLLY BLOOM: And before you hear it. Before you hear it again, I'll give you a hint. This involves something that grows on a tree.


All right. Tobias, what is your guess?

TOBIAS: Ooh. Now after that hint, I'm not so sure.

MOLLY BLOOM: Did I throw you off? Last time you thought, maybe it's like a bag of lentils or corn or something like that.


MOLLY BLOOM: What else do you think?

TOBIAS: Maybe it's like raking leaves or something? I don't know.

MOLLY BLOOM: That's a good guess. Mattia, do you have any thoughts? Any new thoughts?

MATTIA: Raking leaves or maybe cutting a tree? Cutting down a tree with a saw.

MOLLY BLOOM: Yeah cutting a tree with a saw or raking leaves. Those are both really good guesses. Here with the answer is our pal Ruby Guthrie.

RUBY: That was the sound of juicing a lemon.

TOBIAS: Juicing a lemon?



TOBIAS: Oh, I've done that before. But clearly, I haven't done it often enough.

MOLLY BLOOM: Well, you probably weren't really paying close attention to what it sounded like. You were probably just more focused on getting all the juice out. But sometimes you can cut a lemon and a half, and then you put it on one of those juicers where you kind of rub it back and forth. And that's what's making that sound.



RUBY: I brought this sound because, when life gives you lemons, you make invisible ink.

MOLLY BLOOM: Oh, invisible ink. That's a type of ink that dries clear, so you can't see what's written until you heat it, and the words are revealed. Perfect for writing super-secret messages.

RUBY: Exactly. It's something you can try at home. And if you want to make some invisible ink, follow these steps.


You take half a lemon--


--and squeeze all the juice in a bowl.


Now add a few drops of water.


And mix it up.




Ink done. Now take a white piece of paper and find something to dip into the ink. It could be a cotton swab, a toothpick, a paintbrush, even a feather. Then you just dip--


--and write.


And dip--


--and write.


The ink will dry clear. But if you hold your message up close to a lamp--


--the message will reveal itself.

MOLLY BLOOM: Whoa. The ink is turning brown. It is just like magic.

RUBY: More like magic science. Lemon juice is acidic, and when it heats up, it oxidizes and turns brown. Kind of like when you leave apple slices out.

MOLLY BLOOM: Sneaky science strikes again.



SPEAKER 4: My fellow ink appreciators, your love for ink verses is unbound. Just like the best notebooks.


Our encore round of poems is here. This is Ileana from Indiana. She has kindly agreed to perform this rhyme she wrote.


ILEANA: Oh, ink, how it is pink. It is bright and light. It just is so good to write.

SPEAKER 4: Such crisp rhymes. Now as we bring this wonderful evening of ink poetry to a close, we have Norah and Elise from Ashland, Wisconsin. I think they did a great job of summing up the feeling we all share about the inky things in the world. Let's see if you agree.


NORAH: Ink is the best.

ELISE: Red ink is red.

NORAH: Blue ink is blue.

ELISE: Ink is the best.

NORAH: And, ink, I love you.



SPEAKER 4: So touching. Oh, and so true. And, audience, don't worry. If this didn't quite quench your thirst for ink poetry, I am happy to share that we have even more Ink Outside The Box. We'll be featuring some of our contributors' artwork and rhymes at the Brains On Instagram account. Just search for brains_on.



MOLLY BLOOM: People have been using ink for centuries.

MATTIA: And they used all kinds of pens. From early ones made of reeds and feathers.

TOBIAS: To more modern pens like the fountain pen and ballpoint pen.

MOLLY BLOOM: Squids and other cephalopods make ink in their ink sacs, and it's mostly used for defense.

TOBIAS: Tattoo ink is too big for your body to break down, so it stays in your skin.

MATTIA: But these days, you can break it down with lasers that help remove tattoos.

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

MATTIA: It was produced by Marc Sanchez, Menaka Wilhelm, Sanden Totten, and Molly Bloom.

MOLLY BLOOM: We had production help from Paulina Velasco, Ruby Guthrie, and Christina Lopez. And engineering help from John Miller. Special thanks to Charlene and Kendall at [INAUDIBLE]. Stuart Bloom, Taylor Kaufman, and Zack Lupton.

TOBIAS: Now, before we go.

MATTIA: It's time for our Moment of Um.

ECHOING VOICES: Um, um, um-um. Um, um um-um. Um, um, um um.


TOBIAS: What happens to snails when you put salt on them, and why?


TIM: My name is Tim Pearce, I'm curator of mollusks at Carnegie Museum of Natural History.


Sometimes people ask, what happens if you put salt on a snail? First, I would say, it's really pretty cruel. Imagine what would happen if you put salt up your nose. Probably not very comfortable. Well, the outside of a snail is like the inside of your nose. It's a mucous membrane.

So mucus is another name for the slime in your nose, or the slime on the outside of a snail. So the snail is producing mucus, just like your nose is. And when you put something irritating in your nose, like salt, then you produce more mucus. Same thing with the snail. So if you put salt on the snail, the salt is irritating for the snail, and the snail will start to produce mucus to try and get rid of the salt or get away from the salt.

If you put a little bit of salt on a snail, then the snail can probably counteract it and maybe crawl away before anything bad happens. But if you put enough salt on a snail, it will exude so much mucus that it'll kind of dry up the snail. So it's a pretty cruel death.

When snails make mucus for crawling, or for defense, or anything like that, mucus is actually mostly made of water. Just to crawl around, snails have to use an incredible amount of water. In fact, somebody has described snails as these very improbable animals. They're like a leaking bag of water trying to survive on dry land.


MOLLY BLOOM: It's time before the Brain's honor roll. This is how we thank the incredible listeners who keep this show going by sharing their questions, ideas, mystery sounds, drawings, and high fives with us.




Brains On will be back soon with more answers to your questions.

TOBIAS AND MATTIA: Thanks for listening.

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