Play Aggression - often it is possible to see a change in your cat's behavior that will signal to you that the play session is getting out of control. The first sign may be intense movement of the tail from side to side. The ears may go back and the pupils, the dark part of the eye may become larger. At this point it is best to end the play session before the cat becomes too agitated. If you have a cat that likes to hide behind a door and attack when you walk by, you can toss a small toy to divert the cat to an appropriate play object.