A frog uses its whip-like tongue to snag its prey faster than a human can blink, hitting it with a force five times greater than gravity. How does it hang onto its meal as the food rockets back into its mouth?
A new Georgia Institute of Technology study says the tongue's stickiness is caused by a unique reversible saliva in combination with a super soft tongue. A frog's saliva is thick and sticky during prey capture, then turns thin and watery as prey is removed inside the mouth. The tongue, which was found to be as soft as brain tissue and 10 times softer than a human's tongue, stretches and stores energy much like a spring. This combination of spit and softness is so effective that it provides the tongue 50 times greater work of adhesion than synthetic polymer materials such as sticky-hand toys.
The Georgia Tech researchers filmed frogs eating crickets in super-slow motion to better understand the physics of the tongue. They also collected saliva samples and poked the tissue to measure softness.
"The tongue acts like a bungee cord once it latches onto its prey," said Alexis Noel, a Georgia Tech mechanical engineering Ph.D. student who led the study. "It deforms itself as it pulls back toward the mouth, continually storing the intense applied forces in its stretchy tissue and dissipating them in its internal damping."
This tissue damping, Noel said, is much like a car's shock absorbers. The tongue's softness also allows it to change shape during contact and immediately afterward while retracting.
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