Why cats wag their tails. Most people imagine that if a cat wegs its tail it must be angry-but it's really in a state of conflict. The cat wants to do two things at once but each implulse blocks the out and the door is opened to reveal a downpour of heavy rain, the animal's tail may start to wag. If it rushes out and stands ther getting drenched, its tail wags even more furiously. The conflict is between the urge to explore and the powerful feline desire to keep snug and dry. Once the cat makes a decision and either returns to the shelter of the house or sets off on patrol. its tailwill immediately stop wagging.