A transparent inner eyelid is called the nictating membrane. It protects the frog's eyes when the animal is underwater. :-) If you've ever noticed a frog blinking when it eats, it's because it uses its eyeballs to swallow. It can't chew its food effectively, or use its tongue to push food down its throat, so instead it uses its eyes. The eyes sink down into the skull, pushing the food along..!! :-D From: animal.discovery.com/tv/vanishing-frogs/anatomy/frog-eyes...