The amphibians' saliva is what's known as a "shear-thinning fluid," like ketchup—sometimes thick, sometimes thin and flowing. Christopher Intagliata reports.

据克里斯托弗·因塔利亚塔（Christopher Intagliata）报道，两栖动物的唾液是所谓的“剪切稀化液体”，就像番茄酱一样——有时候稠密，有时候稀化而流动。

撰文\播音：克里斯托弗·因塔利亚塔（Christopher Intagliata）

翻译：杨枭

审校：丁可含

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 accelerations?"

你可能认为青蛙能抓住昆虫是因为它们的舌头是粘的。“但为什么舌头是粘的呢？它是如何黏住这些高速度的昆虫呢？”

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 dissection lab, and tested their consistency. Ten times softer than human tongues. A texture more like brain tissue. "Their tongue is very much like a sponge. It's infused with this thick, viscous saliva."

亚历克西丝·诺埃尔（Alexis Noel）是佐治亚理工学院的机械工程博士，她想要回答这些问题。为此，她和她的团队从解剖实验室得到了青蛙舌头，并测试了它们的粘稠度。它们比人类舌头软十倍，质地更像脑组织。“它们的舌头非常像海绵，充满了浓密粘稠的唾液。”

That saliva was their next study subject. "And in order to test the saliva we had to get about a fifth of a teaspoon 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 viscosity. And they found that frog saliva is what's called a 'shear-thinning fluid'—its viscosity changes, depending on conditions.

唾液是接下来的研究课题。“为了测试，我们取来约五分之一茶匙的唾液，对青蛙来说这是很大的剂量。”她们把唾液置于一种可以测量粘稠度的流变仪中，并发现青蛙唾液是 “剪切稀化液”，其粘稠度可以随环境条件改变。

You might be more familiar with a different shear-thinning fluid. "Ketchup. When you smack the bottom of the ketchup bottle you're actually invoking 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."

你可能熟知另一种不同的剪切稀化液。“番茄酱。当你打碎番茄酱瓶的底部，你实际上调用了番茄酱本身的剪切力。 而番茄酱本身，因为它的剪切稀化作用而粘度下降，因而更容易滑出瓶子。”

So back to our frogs: the tongue shoots out, hits the bug and deforms around it. That impact is like a smack on a ketchup bottle—it changes the saliva from thick and sticky to more watery, 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 weird.

所以回到我们的青蛙：舌头伸出，粘住昆虫，然后用舌头将其卷住。这就像番茄酱瓶子碎裂——唾液由粘稠变稀，自由地流过整个虫子。然后舌头像蹦极绳一样弹回来，唾液再次变粘稠。下一步更是奇怪。

"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 Interface. [Alexis C. Noel et al., Frogs use a viscoelastic tongue and non-Newtonian saliva to catch prey]

“青蛙实际上是带着球根眼球，把它们放进口腔，并用眼球把虫子推到喉咙里。”那个力又把唾液稀化，“使昆虫从食管滑下。”该研究发表在了期刊 Royal Society Interface.

With the case closed on this one, Noel's next inquiries 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."

随着这项研究结束，诺埃尔接下来将关注紧握着的指间、耳垢的集尘性能，还有猫的舌头。“是的，我整天付费观看猫的视频。”