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People often talk about having “puked their guts out” after a particularly nasty stomach bug or overindulging in tequila shots. But, of course, humans don't actually do that.

It's just a metaphor we use. But some animals do throw up their entire stomachs! Which is gross, but also, a really great example of how the same trait can evolve in many species for a variety of reasons.

We've all been there— you're so sick that it feels like your entire stomach is going to end up in the toilet. Vomiting is a common behavior in vertebrates since it helps eject bad stuff like poisonous substances. But no matter how sick you are, your stomach remains securely in your body, thanks to your lower esophageal sphincter, or LES— a ring of smooth muscle between the esophagus and the stomach.

It helps you keep your meals where they belong, too. It's why you can lay down or even stand on your head after a large meal without food coming back out your mouth. So, thanks LES.

But sometimes, you do want what's in your stomach to... not be in it anymore. So the LES can relax and allow you to up-chuck. Frogs and toads, on the other hand, don't have an LES.

And that means, when they vomit hard, their whole stomach can come out— though it doesn't always. Still, it turns out being able to puke out your guts is kind of useful. Just vomiting doesn't always expel things super effectively— like, say, if you're trying to puke out a living wasp or poisonous insect, which in addition to being harmful, can be kind of grabby.

So, when some frogs and toads ingest those things, they throw up their entire stomach. It's called stomach or gastric eversion, meaning “to turn inside out.” And that's exactly what happens. Since there's no distinct boundary between their esophagus and stomach, their stomachs can flop out of their mouths, kind of like turning a pocket inside out.

The prolapsed stomach then kind of hangs there, allowing the animal to literally wipe away anything that might be clinging to their stomach walls. Weirdly enough, it seems like frogs and toads usually use their right hand for this. See, even though they don't have an LES, their stomachs are still attached to their abdomens by a continuous band of tissue.

And the bit attached to the right side of their stomachs is shorter. So as the stomach everts, it's pulled to the right. Frogs and toads aren't the only animals that can evert their stomachs, though.

Sharks and rays do this, too— and probably for similar reasons. Many species dine on animals with bones or shells— materials which don't digest well, so little bits can get kind of stuck in the mucous-y lining of their stomach . So, they might just flip the whole thing out every so often to remove this debris.

In an article published in 2000, for example, researchers from the UK observed a thornback ray rinsing —or vomiting up—its stomach nine times just minutes after it was given a barf-inducing food. Not only that, but much like how frogs and toads use their hands, sharks may use the edge of their mouths to wipe their stomach linings during eversion ——at least, according to one observational report from 2005. But there might be another reason some species are so quick to puke their guts out.

Sharks will also vomit when they're stressed, and while they don't always perform gastric eversion, sometimes, they do. And scientists believe this may be a defense mechanism. Basically, it's easier to get away when your stomach is lighter and emptier.

In terms of puking to defend themselves, though, sharks have nothing on sea cucumbers. Many sea cucumbers engage in a strategy called autotomy: they sacrifice parts of bodies to distract or ensnare a threat. It's kind of like how some lizards detach their tails, but in this case, the “parts” being sacrificed are the cucumber's internal organs.

They literally eviscerate themselves. For some species, this happens out the rear end and involves sticky parts that can trap predators. So, I guess you could say, poop their guts out.

But other species do puke their guts out. When under attack, they eject pretty much their entire digestive tract— including intestines!— out of their mouths. Some also lose parts of their mouths, like the tentacles they use to snag their food.

And they may even barf up their gonads! The idea is that these bits of them either gross out a hungry attacker or distract them long enough for the cucumber to make a slow escape. You might think losing your innards would be kind of a problem, but the cucumber doesn't care what it sacrificed from what end, because it can regenerate its internal organs in a matter of weeks.

Scientists are actually studying their incredible regeneration abilities in the hopes of helping people after injuries or figuring out how to grow transplantable tissues and organs. Now, between sea cucumbers, sharks, and frogs, you might think puking your guts out is a protective strategy. But sea stars barf their stomachs out offensively to devour prey.

Sea stars actually have two stomachs: the cardiac stomach and the pyloric stomach. When a star finds something to eat, it pushes its cardiac stomach out of its mouth— which, by the way, is located on the underside— and at this point, right on top of its future meal. It can even squeeze this stomach into a small gap in a clam or mussel shell if necessary.

The everted stomach then does what stomachs do best— it secretes digestive enzymes which break down the prey into a soupy, chowder-like substance, which it'll absorb back into its body's ten digestive glands. The cardiac stomach is then pulled back through the mouth, and the food is transferred to the pyloric stomach to finish digesting. So yeah—lots of animals puke their guts out.

But they don't all do it for the same reasons. Let's just be glad we don't wipe our stomach linings whenever we eat something that's a little bit off. If you're eager to learn more about vomiting— and who isn't?!— you might want to check out our episode on why kids puke so much.

And if you're just eager to learn, period, consider clicking that subscribe button and ringing the notification bell. That way, you'll get an alert every time there's a new SciShow episode to watch. [ outro ].