Cat tail movement can tell you a lot about how your cat is feeling and what it is about to do. Cats frequently use their tail for communication, and knowing what those signals mean can help you interpret your cat's emotions and make him more comfortable.
Normal Tail Movements
The cat's tail is an extension of his spine, which is required for posture and balance. Thus, a calm, content cat will usually hold its tail upright, possibly slightly curved above his back to avoid getting it caught on objects.
When happily greeting strange humans or cats, a straight, upright tail indicates a friendly cat. If the tail is slightly curved, it may indicate some uncertainty, but the cat is still generally comfortable. A lowered tail generally indicates the potential for aggression.
Happy Tail Twitching
Tail twitching generally indicates displeasure in your cat, a sharp contrast to the happy tail wagging of a dog. However, cat tail twitching can sometimes indicate pleasure as well.
Cat tails often raise up and quiver when a cat is spraying its scent. Once cats are spayed or neutered, the spraying will discontinue, but the behavior often persists, particularly when their owners return. This indicates happiness or excitement.
Cats may also swish their tails if they are interested in something and may take action at some point. This might not necessarily indicate aggression, though it can. The more violent and fast-paced the swishing becomes, the more excited the cat is. This tail action can also be used to initiate play with another cat.
Angry Tail Twitching
Cat tail twitching is most often associated with aggression and hunting, so though you may know your own cat greets you with a quivering tail, avoid a strange cat that wags its tail.
A cat with a straight tail twitching back and forth deliberately is usually issuing a threat. He is displeased with your actions and warning you (or another cat) to stay back and avoid a conflict.
Cats may also have a slight twitch when hunting. During this time, the cat will usually be crouched low to the ground and focusing on its prey. The twitching tail is an indicator of intense focus. You may notice a slight twitching in the tip of your cat's tail when he looks out the window. This usually means he has spotted prey, even if he can't hunt it.
A sweeping tail alerts you that a cat is readying himself for action. If the cat is at rest but twitching its tail, he is often deciding if he wants to take action. As he gets closer to taking action, the tail movements will become faster, wider and more deliberate. While this generally predicts some form of aggression, it can often indicate high excitement, as listed above. Thus, your cat may show this tail movement if it is enjoying a grooming session or game of play.
Though a wagging tail usually indicates friendliness in dogs, this is not true of cats. If you encounter a stray cat with a twitching tail, avoid it, as it usually predicts aggression.