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Snakes don’t have lips, they can't lap up water, and they don’t grab mouthfuls of water and tip their heads back to swallow, so how do they drink? Turns out, some snakes have sponge-mouths that literally soak up water!

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[♪ INTRO].

Have you ever looked at a snake and wondered: how does this thing drink? Well, animal physiologists certainly have.

And the answer isn't obvious. Snakes don't have lips like we do. And it's pretty clear that their skinny, forked tongues weren't built for lapping up water.

And they also don't grab mouthfuls of water and tip their heads back to swallow. Back in the 1990s, researchers thought they'd figured this conundrum out. But it turns out they missed something.

And that something was that at least some snakes have sponge-mouths that literally soak up water. Those scientists in the 90s carefully watched boa constrictors, brown tree snakes, and eastern rat snakes while they drank. And between videos and some fluid dynamics modeling, they determined that the animals were relying on suction.

Essentially, by rhythmically contracting certain muscles in their mouths and throat, they could suck water up and push it back continuously without having to tilt their heads. And this mechanism works because the snakes can seal their mouths shut to drink, kinda like when you close your lips around a straw. But then researchers observed snakes drinking without sealing their mouths.

Which just didn't make any sense, until they realized that their mouths were basically sponges. You see, the floor and the roof of a snake's mouth are covered in soft tissues with lots of folds. And, it turns out the animal can expand the space between those folds ever so slightly.

The molecules coating these tissues are really good at attracting water. And that attraction, called adhesion, is stronger than the water's attraction to its own molecules, or cohesion. So, as the snake opens its mouth to allow water in, it expands these folds, and by a process called capillary action, water molecules can be drawn up and in against gravity.

It's essentially the same as what happens with a sponge. If you put a squeezed one on a wet spot and then slowly release, the water will travel up and in. And once the animal's skin-sponge is nice and wet, further movement of the bones and muscles in the jaw and head will compress the mouth.

This squeezes the water out from the folds so it can be swallowed. Now, this sponge-like drinking likely occurs alongside the more active suction-drinking, rather than instead of it. And it seems to be totally unique to snakes, even though some lizards have similar folds of mouth tissues.

That tells us that they probably didn't evolve these folds for drinking. More likely, they're what biologists call an exaptation: a trait that evolved for one purpose, but now serves another. Scientists think they exist because snakes swallow their prey whole.

To do that, their jaws need to open incredibly wide and wrap around their meal, hence, expandable skin. So these folds probably evolved for eating, and they just happened to be pretty useful for drinking, too. And there's probably more to this story.

The truth is, scientists are still not completely sure how snakes drink. Some species seem to use both these methods, others favor one, and some might switch things up as they get older and grow bigger. So it turns out that snake drinking is still a bit of a puzzle!

But what we do know is cool and weird, and just, I mean, sponge-mouths. That just doesn't even seem real! Thank you for watching this episode of SciShow.

And if you want more jaw-dropping snake facts, be sure to check out our episode on 6 extraordinary serpents. And, if you just want a little more science in your life in general, go ahead and click that subscribe button. Or, you can check out our other channels, SciShow Space and SciShow Psych! [♪ OUTRO].