Machat b'Ovi Beis ha'Kosos - only makes a Tereifah if there is a drop of blood. Otherwise we will assume that it came afterwards.
My question is that on 49a on top the Gemara asks why it is Kosher if there is a hole only on one side, why aren't we afraid that the needle came from the outside.... (see the answer there).
If there is such a possibility, then why don't we prohibit the animal with a hole in the Beis ha'Kosos and no blood because of the needle, which must have punctured some internal organ when it entered!
Yossi Katz, Yerushalayim
1. The Gemara (beginning of 49a) asks that the animal should be a Tereifah only because the Gemara there is referring to where there is a drop of blood. If there would have been no blood, it would have been clear to the Gemara that the puncture must have happened after Shechitah, and the animal is Kosher.
This is clear from the Mordecahi (#527) here, who writes that even if the needle sticks through from one end to the other, a drop of blood is still necessary in order to determine that the puncture happened before Shechitah.
2. However, the Hagohos Ashiri (end of Rosh #34) disagrees with the Mordechai. He writes that since the needle has penetrated all the way through, even if there is no drop of blood on it the animal is a Tereifah. See the Bi'ur on the Maharam Shif (50b, #8) who elucidates how the Maharam Shif explains the Hagahos Ashiri so that his words not contradict the Beraisa which states that if there is no drop of blood on the needle, the animal is Kosher. The difference is that if the needle is only seen to have pierced one side of the Beis ha'Kosos, then the animal is a Tereifah only if the blood is directly on the tip of the needle, which is a very strong proof that the puncture happened when the animal was alive. In contrast, if the needle is seen to have gone through both sides, then it is a Tereifah even if the blood is merely near the hole. (According to this explanation, when the Hagahos Ashiri writes that even if there is no drop of blood on it, this means that the animal is a Tereifah even if the blood is not directly on the tip of the needle.)
It follows that the Gemara earlier (beginning of 49a) also refers to a scenario in which there is blood on the needle, but now it depends exactly where the blood is. If the needle is found only on one side, then the animal is kosher as long as the blood is not directly on the point of the needle, but if the needle has gone all the way through, the animal is a Tereifah as long as the blood is near the hole.