They then usually eat the old skin. Frogs have fairly good eyesight, which helps them in capturing food and avoiding enemies. A frog's eyes bulge out, enabling the animal to see in almost all directions. Frogs can close their eyes by pulling the eyeballs deeper into their sockets. This action closes the upper and lower eyelids.
Most species also have a thin, partly clear inner eyelid attached to the bottom lid.
This inner eyelid, called the nictitating membrane, can be moved upward when a frog's eyes are open. It protects the eyes without completely cutting off vision. Most frogs have a disk of skin behind each eye. Each disk is called a tympanum, or eardrum. Sound waves cause the eardrums to vibrate.