Aggression is a normal part of predation and a consequence of an emotional state. However, if cats start to show aggression towards humans, this could constitute 'problem behaviour'.
Knowing the basic postures enables you to understand your cats' feelings. It also helps you respond more effectively to behaviour issues like aggression, which can be primarily either offensive or defensive.
When cats perceive a threat, aggression escalates if they can't escape.
When cats feel an intruder is infringing on their territory. Whilst often directed at other cats, people and other animals may also be the subject of the aggression.
It involves typical predatory behaviours, including stalking, chasing, attacking, running, ambushing, pouncing, leaping, batting, swatting, grasping, fighting and biting.
When cats are aroused and agitated by an animal or person they can't get at (e.g. there's a window between them). Unable to get to the trigger of their agitation, they turn and lash out at someone - person, dog or cat - who is nearby or approaches them.
When cats who enjoy being pet suddenly change their mind. It's thought that the repetitive motion over time turns from pleasant to irritating.
Even well-socialised cats can lash out when someone tries to touch a painful part of them.
According to ASPCA, a number of medical conditions can cause or contribute to cats' aggression, including toxoplasmosis, hyperthyroidism, epilepsy, abscesses, arthritis, dental disease, rabies, trauma, and sensory decline or cognitive dysfunction in older cats. The first step in resolving your cats' aggression problem is to have a complete veterinary exam to assess their physical health.