The most common type of aggressive behavior is play aggression, which is normal for all young mammals. For cats, play aggression includes stalking, pouncing, and mock fighting. A young cat may hide in a corner and then stalk, chase and pounce on an object or person! Kittens normally play with each other, with their mother and with a variety of moving objects. If none of these are available, they will treat human arms and legs as playthings.
It's important to teach kittens an acceptable way to play right from the beginning. If possible, take home two kittens so they can fulfill their need to play with each other. If this is not feasible, then direct the kitten to "fun" toys such as long strings with toys or feathers attached (don't let your kitten swallow it!) or ping-pong balls. This will help minimize those secret ambushes, and prevent you from becoming, in effect, a big squeaky toy. Always keep these toys, especially the ones with strings, away from your cat when you are not around to supervise. Many people misinterpret play as a sign of serious aggression. Playful cats "attack" silently and do not typically break the skin when they bite. Seriously aggressive and potentially dangerous cats often hiss or growl and bite more severely. Using a water spray bottle to keep the cat at bay is sometimes a helpful temporary measure. Hitting a cat is not recommended since it often causes a defensive reaction, may lead to aggression, and is inhumane.