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You might think frogs catch insects ‘cause their tongues are sticky. "But why is the tongue sticky, and how does it actually adhere to these insects at these very high accelerations¹?"

也许你认为青蛙能捕食昆虫是由于舌头很粘的缘故。但是为什么它们的舌头是粘的，同时舌头是如何在昆虫快速移动的时候黏住它们的呢?

Those are the questions Alexis Noel, a PhD candidate in mechanical engineering at Georgia Tech, wanted to answer. So she and her team got frog tongues from a dissection² lab, and tested their consistency³. Ten times softer than human tongues. A texture⁴ more like brain tissue. "Their tongue is very much like a sponge. It's infused with this thick, viscous⁵ saliva⁶."

亚历克西斯·诺埃尔，是佐治亚理工大学的机械工程专业博士研究生。他想要回答上述问题。所以和研究团队从解剖实验室获取了一些青蛙的舌头，并且检测了这些舌头的的粘度。青蛙舌头的柔软性是人类舌头的十倍之多。纹理更像大脑组织。“青蛙的舌头就像一块海绵。充满了粘稠的唾液。”

That saliva was their next study subject. "And in order to test the saliva we had to get about a fifth of a teaspoon⁷ of fluid. Which is a lot of saliva, in a frog's case." They put the saliva in a rheometer, a tool that can measure viscosity⁸. And they found that frog saliva is what's called a 'shear⁹-thinning fluid'—its viscosity changes, depending on conditions.

青蛙的唾液是他们下一个研究的课题。“并且为了检测这些唾液，我们收集了五分之一茶匙的青蛙唾液。对一只青蛙而言，这些唾液的量很大了。之后，他们将这些唾液放入了一个流变计，这是一种可以检测粘稠度的工具。结果研究人员发现，青蛙的唾液是一种“剪切稀化的液体”——也就是说其粘度取决于外部环境。

You might be more familiar with a different shear-thinning fluid. "Ketchup¹⁰. When you smack¹¹ the bottom of the ketchup bottle you're actually invoking¹² shear forces within the ketchup itself. And ketchup, because it's shear thinning, its viscosity actually drops and allows it to slide out of the bottle easily."

也许你对另一种剪切稀化的液体更为熟悉。番茄酱。当你拍打番茄酱瓶底部时，实际上是在激发番茄酱内的剪切力。由于番茄酱剪切力很弱，它的粘度就会降低，然后就很容易从瓶子上滑下来。

So back to our frogs: the tongue shoots out, hits the bug¹³ and deforms¹⁴ around it. That impact is like a smack on a ketchup bottle—it changes the saliva from thick and sticky to more watery¹⁵, free to flow all over the bug. Then the tongue bounces back, like a bungee cord, and the saliva thickens up again. What's next is beyond weird¹⁶.

现在回到我们的青蛙的问题上：舌头突然伸出来，碰到虫子，绕着虫子变形。这种影响就像是你轻拍番茄酱瓶底——它使唾液从高粘稠度转变为像水一样稀，轻易自由的流过虫子的全身。然后舌头像一个弹簧绳一样被拉回，然后唾液再次变得粘。接下来也就不奇怪了。

"Frogs actually take their bulbous eyeballs and bring them down into their mouth cavity and use their eyeballs to shove the insect down the throat." That force turns the saliva watery again, "and the insect slides down the gullet." The study is in the Journal of the Royal Society Interface¹⁷.

青蛙将眼球压入口腔，将昆虫从舌头上压入腹中。”这种眼球产生的挤压力让舌头上的唾液再次液化，使昆虫与舌头分离，然后昆虫就顺流滑入食管。该研究已经发表在《皇家学会界面》杂志上。

With the case closed on this one, Noel's next inquiries¹⁸ are on grippy fingertips. The dust-collecting properties of earwax. And—wait for it—cat tongues. "Yeah, I get paid to watch cat videos all day."

这个课题就此结束，诺埃尔博士下面的研究内容是粗糙指尖。耳垢的集尘特性。还有，等等，猫舌头。是的，有人给我钱，让我整天看猫咪的视频。