When it comes to really big lizards, people often confuse the alligator with crocodiles. Two of the easiest ways to tell them apart, has to do with their location and their teeth.
Alligators are a freshwater creature, and can be found in rivers and ponds, inland. Crocodiles prefer the brackish, dank semi-salt content of coast ponds and bayous. Their general appearance is somewhat different, but when confronted by what appeared to be a log, steaming towards them, few people stop to remember that the dark-colored alligator has a head that is broad, with a round snout. The crocodile has a narrow head that ends in a tapered and pointed muzzle.
Then there are the teeth. Even if they aren't yawning at you, it's easy to tell them apart, because on a crocodile, the fourth tooth on each side of its jaw, sticks out and above the skin. Alligators have an empty socket in the upper jaw where these teeth slot in when their mouth is closed, which keeps them hidden.
Those big teeth see a lot of work over a lifetime, as well. Although the alligator only has around 80 teeth at any one time, as they are worn down, another grows underneath and replaces it. In their natural lifespan of 30-35 years in the wild, one alligator can go through about 3,000 teeth.