Feline body language is not intended to deliver refined signals. The messages are broad, such as "Leave me alone." Triggered by fear, a rush of adrenaline causes the cat's back and tail to arch and the hair to bristle. This familiar Halloween-cat pose makes the frightened feline appear more physically imposing. Although the raised hackles may outwardly convey strength and a readiness to do battle, the communication is really designed to dissuade rather than provoke potential attackers. When cats, wild and domestic, are fearful or nervous and defensive, their ears flatten or twitch and their eyes dilate fully to take in as much of their surroundings as possible.

The body language of confident, aggressive cats is exhibited in response to direct confrontations, with intruders on their territory or run-ins with smaller cats. The pupils narrow to slits for better depth perception as they stare down opponents; their ears stand up, facing forward or folded so that the backs are seen head-on. With its rear end held high and tail slung low, an aggressor will often approach the defensive cat in a prancing sideways motion that creates the illusion of being larger.

Not all feline body language is straightforward, however. Messages sometimes seem to be mixed or conflicting. Since most of a cat's body language is not intentional but a reflexive response to stimulus, anger and fear may elicit the same physical response. It is not unusual, for instance, for a fearful feline to display signs of aggression and vice versa.