House soiling in cats, also called feline inappropriate elimination, is the most common behavioral complaint of cat owners. Problem behaviors can be urine and/or stool deposited outside of the litter box, or marking behaviors. When cats urinate on vertical surfaces, it is known as spraying. Usually, the cat backs up to a vertical surface, raises its tail, which may quiver, treads with its back feet, and directs a stream of urine backward. Marking includes spraying urine on vertical locations; on occasion, a cat may mark its territory by urinating small amounts on horizontal surfaces.