What causes cats to chatter when they see birds?

Cats have a variety of unusual vocalizations that are frequently amusing, but chattering represents one of the most intriguing vocal expressions. A cat's chattering causes a quick stuttering, clicking, or trembling of the jaw. Tweets and chirps that are brief, quiet, or high-pitched are frequently heard along with them. When a cat spots an interesting prey animal, like a bird or a rodent, outside a window, it typically chatters.