"but also to those animals, which, though in the "clean" category, are ritually unclean there are situations in which the animal itself is kosher - like a chicken, and it is permissible to eat it but- it's possible that the slaughtering process wasn't done properly. or it may have a damaged organ in its body-like type of cavities or infections in the lungs- which makes the animal or bird impure- it's also unhealthy- but this is from the aspect of the law 