In a study performed in 1987 it was reported that cats who fall from less than six stories, and are still alive, have greater injuries than cats who fall from higher than six stories.[6][7] It has been proposed that this might happen because cats reach terminal velocity after righting themselves (see below) at about five stories, and after this point they are no longer accelerating, which causes them to relax, leading to less severe injuries than in cats who have fallen from less than six stories. Another possible explanation for this phenomenon is that cats who die in falls are less likely to be brought to a veterinarian than injured cats, and thus many of the cats killed in falls from higher buildings are not reported in studies of the subject.[3]