It ranges from drab green or brownish to a blackish tone on the dorsal side and is much lighter, and softer, on the ventral surface. Crocodiles can be distinguished from alligators by their long narrow snout and their fourth mandibular tooth, which protrudes from their lower jaw rather than fitting in to their upper jaw. The eyes and nostrils of crocodiles are situated on the top of the head so they can see and breathe while the rest of their body remains almost totally submerged. Unlike other reptiles, crocodiles have external ears that close, along with the nostrils, when they dive. Another feature that helps the crocodile survive in the water is its third, transparent eyelid, which it closes while diving to keep water out of its eyes without sacrificing its vision.
Crocodiles swim using their enormous, oar-like tail.
Only their rear feet are webbed, and they are rarely used in movement underwater. On land, the crocodile walks on its short, seemingly weak legs. They bring their legs in close to their bodies and lift themselves high off the ground when walking. They plant their front feet, bring their hind legs around the outsides of the front legs, plant them, and then lunge forward with their front legs. Nile crocodiles have been known to reach speeds of up to 29 miles per hour.