Watching birds or squirrels, cats often emit rapid chirps with a trembling jaw, a behavior called chattering that is very common indoors.
The leading explanation blends hunting arousal with the frustration of unreachable prey, and some propose the jaw motion rehearses the killing bite; it remains unsettled.
A sturdy window perch enriches an indoor cat's day, but verify screen strength and fall protection before letting a cat lunge at birds.
Frustration can occasionally redirect onto housemates, human or feline; when the cat is tense and tail-thrashing at the window, simply avoid touching it.
