ASPCA: Animal Behavior Center: Cat Behavior: Urine Spraying
Cats sometimes engage in a behavior called urine spraying or urine marking. The cat stands, backs up to an object, holds his tail up erect and quivering, and releases urine out backwards onto the object. The urine sprayed differs chemically from the urine cats normally release from a squatting position because it also contains oily secretions from the anal glands. Sprayed urine is extremely pungent. Some people describe it as smelling like ammonia; others say it has a heavy musky odor. Cats occasionally spray from a squatting position.