Tail wags and twitches in cat's tails are common. A tail swishing back and forth rapidly indicates both fear and aggression. If a cat's tail is gently swishing from side to side it may indicate that your cat is interested and alert to something that is happening.

What does it mean when a cats tail swishes?

A cat's tail beating back and forth violently and rapidly usually signifies aggression. This kitty is no happy camper and someone or something is about to feel her wrath. A quickly swishing tail usually means that a cat is ready for attack. ... Leave any cat in this emotional state alone for a while.

Is a cat happy when it wags its tail?

Cats Wag Their Tails When They're Happy and Confident

Sometimes she'll also slightly curve the tip of her tail and even twitch or wag it softly. This isn't the same exuberant tail wag dogs use, but it's a subtle way to let you know she's happy and content.