Due to a restrictive membrane, crocodiles can't stick out their tongues. This membrane keeps the crocodile's tongue attached to the roof of its mouth rather than the base. The inability to stick out their tongues differentiates crocodiles from their relatives, the alligators.
Because of the unique anatomy of the crocodile's tongue and the tissue called the palatal flap at the back of the throat, a crocodile can keep out excess water or air that sifts through its teeth. Because of this, crocodiles, who primarily hunt underwater and use their mouths to catch prey, can open their mouths below the surface in preparation for a kill. Crocodiles also have a salt gland in their tongues and an opening on the tongue's surfaces.