Chullin 50 - Intestines, Rectum
If the intestines are punctured, the animal is terefah. However, it is also possible that the puncture happened after the animal was slaughtered. In that case it would be kosher. To find out when did the puncture really happen, one can compare a puncture in the intestines to the new one, made just for the purpose. If they look similar, the first puncture was made by people handling the meat after the slaughter, and the animal is kosher. If they differ, the animal is terefah.
They brought such a case before Rava, who made an additional puncture, and seeing that it looked different, wanted to declare the animal a terefah. His son Rav Mesharshiya said to him, "Think of all the hands that the first puncture went through before it came to you." Rav Mesharshiya then rubbed the new puncture, and it appeared the same as the old ones. Thi showed that the animal was kosher. Rava said, "My son is as wise as Rabbi Yochanan."
If the rectum was punctured, this does not make the animal terefah, because the hips support it. Even if only a finger-width of the rectum remained intact, it is kosher.
Art: Lorenzo Delleani - Wise Counsel