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Reversible Saliva Lets Frog Switch Between Sticking Prey and Swallowing


Good thing our tongue isn't like that of the common frog. If it was, it would stretch one-third of the length of our body — about down to our belly button. On the positive side, we could whip it out and strike an object with several times the force of our own weight. And, scientists now say, we'd have a tongue coated with useful, reversible saliva.

Researchers at the Georgia Institute of Technology recently studied frog tongues to discern exactly how they are able to so quickly and efficiently capture their prey. Their studies revealed two main things: Frog tongues are exceptionally soft and elastic, while the tongues' saliva has the unique ability to switch from thick and sticky to thin and watery.

By being incredibly soft — 10 times softer than human tongues — a frog tongue is able to stretch and store a lot of energy. Enough energy to lash out, snatch a tasty cricket and whip it back in again before we humans can blink an eye. This super-softness also allows the tongue to change shape as it hits its prey and retracts into the mouth, acting like a bungee cord and shape-shifting to distribute the intense forces involved in the process.

The frog's saliva, meanwhile, is busily at work morphing from thin to thick to thin again. When a frog's tongue strikes its prey, the saliva coating its tongue is watery and thin so it can fill all of the crevices in the insect's body. This helps keep a tight hold on the bug. As the tongue retracts, the saliva becomes thick and almost honey-like in consistency to ensure a firm grip on its prey. Once inside the frog's mouth, the saliva reverts to a watery consistency so the insect can easily slip off the tongue and down the frog's gullet. Frog saliva, then, is rather like paint, which spreads easily when you're painting, then becomes firm as it adheres to the wall.

Scientists conducted their research by collecting frog saliva samples and measuring its viscosity in a rheometer, a device that measures the various properties of fluids. They also filmed frogs downing crickets in slow motion, as seen in the video: 

The results were published in the Journal of the Royal Society Interface. Scientists hope the results of their research might help in the development of better adhesive bandages, household tape or even new materials for soft manufacturing.



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