2,578. What We Mean by "Concerned" and "Unconcerned"

Hilchos Shechita 9:17

Whenever we say that we’re unconcerned, it’s permitted to slaughter the animal right away and we don’t need to check if an organ was crushed. Whenever we say that we are concerned, then if one slaughters the animal, he must check all of its internal organ from the head to the thigh of the hindquarters. If any of the aforementioned things that make an animal treif are found, or if one of the internal organs was crushed to the point that its shape is ruined, the animal’s a treifa. This is true even of an organ that doesn’t render an animal a treifa if removed, like the spleen or the kidneys. The exception to this rule is the uterus, which doesn’t render an animal a treifa if crushed.

Hilchos Shechita 9:18

The esophagus and the trachea don’t need to be checked in such cases as a fall won’t crush them.