Scratching provides both visual evidence (claw marks) as well as a scent marker. Cat paws have scent glands that can leave smells that are detectable to other cats and animals. But it’s not just territorial: Cats also scratch to remove sloughed-off nail tips, allowing fresh nail growth to occur. And they can work out their knotted back muscles—cramped from sleeping 16 hours a day, no doubt—by kneading the soft foam of a sectional.