You may think your indoor kitty has no cause to be a grand hunter like his relatives were in the wild, but try telling him that. Artificial selection and breeding of cats by we humans have not blunted the urge to hunt. This desire has little to do with hunger and everything to do with instinct and pure enjoyment.
Sometimes when your indoor cat watches “prey,” like birds or a squirrel, through a window, or sometimes just sees them on television, he makes a chattering sound. The cat opens his mouth slightly, pulls his lips back, and then opens and closes his jaws very quickly. The noise that results is a cross between lip-smacking and teeth chattering. If he is really excited, he might add a vocal utterance that sounds almost like a cry.
That noise is more instinctual than many of us realize. Feline behavioral specialists have noted the similarity of the noise to one made by cats delivering a special neck bite when killing a bird or small rodent. Cats can deliver this bite quickly and efficiently causing death before the prey has a chance to struggle. Young kittens in the wild have opportunities to practice and hone this special bite.
In chattering and squeaking, house cats may be showing their excitement at seeing potential prey, or they may be acting out their frustration in seeing potential prey that they cannot reach. Many times, you may notice that your cat’s tail gets puffy or twitches in a special way that accompanies his special chattering noises.
So when your kitty sits in the window and chatters at the birds, he may be feeling frustrated that he can’t be the hunting critter that he was meant to be. So he practices instead by acting out the fatal bite to his kill.