Alligators as necessarily the most communicative and expressive creatures in the animal kingdom, these big genus Alligator reptiles do indeed have their own distinct ways of relaying relevant messages. From noticeable hissing sounds to inaudible infrasound, alligators certainly know how to get their points across to others. Some species of alligators are capable of communicating even before birth -- think the American alligator (Alligator mississippiensis), to be specific. These reptiles are the most "talkative" crocodilian species, and begin producing high "complaining" noises while living within the eggs. If an alligator is feeling stressed out, anxious, shocked or frightened in general, he may producing a yelping sound, which is a brief crying or whining sound.