Bruce Fogle, DVM addresses what he thinks is going on when a cat's teeth chatter. He believes the cat is frustrated. "When a housebound cat sees a potential meal sitting on the lawn, but can't get near it, he becomes frustrated. He lowers his head, stares intently at his prey and then, either knowingly or not, his teeth move as they would if he had captured the bird. He carries out a death bite but, in the absence of prey, all that happens is his teeth chatter."
I am not sure I am fulling buying into that explanation. Willow doesn't look frustrated when she chatters, she looks like she is scheming how she is going to take down the bird. When a cat bites to kill their prey, is it one death bite or a series of rapid death bites, like what happens in the chatter? This fascinating characteristic to me remains a mystery.
Quote from: 101 Questions Your Cat Would Ask Its Vet If Your Cat Could Talkby Bruce Fogle and illustrated by Lalla Ward. A fun factoid about this book: Lalla Ward, an actress, played my favorite Doctor Who companion, Time Lady Romana, starting in 1979.