A litter box, sometimes called a sandbox, cat box, litter tray, cat pan, or litter pan, is an indoor feces and urine collection box for cats, as well as rabbits, ferrets, miniature pigs, small dogs, and other pets that instinctively or through training will make use of such a repository. They are provided for pets that are permitted free roam of a home but who cannot or do not always go outside to excrete their metabolic waste. Many owners of these animals prefer not to let them roam outside for fear that they might succumb to outdoor dangers. On average, indoor cats have a lifespan of 16.8 years while outdoor cats' lives are much shorter, only 5.6 years. These outdoor dangers include weather, wildlife, traffic or diseases such as the feline immunodeficiency virus.