When the cat is excited, its tail will swing back and forth quickly, which shows that the cat is very excited at the moment. Let the cat leave the exciting environment or object in time, otherwise the cat may jump up and down to catch people. Sick: When a cat is sick, its tail will swing from side to side. If the cat's tail swings from side to side, think about whether you have blamed your cat at this moment. If not, maybe the cat is sending you a message. It is sick. Anxiety: when a cat is anxious, its tail will swing slightly from side to side, and when it is hungry or sleepy, it will swing slightly from side to side to show anxiety.