Cats use their tail movements as a form of communication to express their feelings and intentions. For example, a cat may flick its tail rapidly when it is agitated or annoyed, while a slowly swishing tail can indicate that the cat is relaxed or content. A puffed-up tail may signal fear or aggression, while a straight, erect tail can show confidence or excitement. By observing a cat's tail movements along with their body language and vocalizations, you can better understand their mood and behavior.