Why do cats chatter?

Why cats chatter at prey is not known, but one theory is that they are mimicking the calls of the targeted animal in order to trick them. Cats in the wild have been observed vocally mimicking monkeys. Other theories include that it is an expression of frustration or excitement.

Cats are most often observed chattering at birds, especially after a nearby bird that is inaccessible to the cat has loudly vocalized. Some scientists believe that the chattering is an attempt at drawing the bird closer, or at the very least disguising the presence of the cat. Others believe that the chattering is merely a side effect of the cat repeatedly chomping its teeth together in anticipation of a killing bite. This is thought to be due to either excitement at the presence of prey, or to frustration at the prey being inaccessible.