Aggression refers to threats or attacks. Aggressive acts in cats include hissing, growling, swatting, chasing, and biting. Cats can have various kinds of aggressive behaviors. Non-recognition aggression occurs when one cat is uncharacteristically aggressive toward a companion cat after a period of separation. For example, after one cat returns home from a veterinary visit, the cat that stayed home is aggressive toward the returning cat, who may flee, freeze (hold still), or fight back.
Island Bird Cat & Dog Vet Group