Gemara

(Ula): If a thorn became stuck in the Veshet, we are not concerned lest it punctured the Veshet and the wound healed.

Question: According to Ula, why is this different than a Safek Nidras? (Drisah is scratching with poisonous claws.)

Answer: Also there, Ula is not concerned.

55b (Beraisa - R. Meir): Gludah (an animal without skin) is Kosher;

Chachamim say, it is Tereifah.

(Beraisa - R. Shimon ben Elazar): R. Meir and Chachamim both agree that Gludah is Tereifah, but if skin the size of a Sela remains, it is Kosher.

Question: Where must the skin be?

Answer #1 (Shmuel): It must be along the entire spine.

(R. Nehurai citing Shmuel): The width of a Sela must cover the entire spine.

Answer #2 (Rabah bar bar Chanah): A Sela must cover the vertebrae and the joints.

Answer #3 (R. Elazar ben Antigonus): It must cover the navel.

Questions (R. Yanai b'Rebbi Yishmael): What is the law in the following cases: only the skin covering the spine was removed, or only the skin over the joints, or only the skin over the navel?

These questions are unresolved.

Kidushin 39a (Rav Asi): A tradition from Moshe from Sinai forbids Orlah in Chutz La'aretz.

Question (R. Zeira - Mishnah): One may buy Safek Orlah in Chutz La'aretz, as long as he does not see the seller picking Vadai Orlah. (If tradition forbids it, we must be stringent about a Safek!)

Answer (Rav Asi): The tradition forbids only Vadai Orlah.

Rishonim

Rambam (Hilchos Ma'achalos Asuros 4:6): One who eats a Tereifah animal is lashed for "u'Vasar ba'Sadeh Treifah Lo Sochelu." Tereifah mentioned in the Torah is when a wild Chayah such as a lion or tiger was Toref (tore) it, or a bird that is Dores.

Rambam (Hilchos Shechitah 5:3): Even though all of the Treifos are a tradition from Sinai, since only Drusah is explicit in the Torah, Chachamim were stringent about it. Every Safek about Drusah is forbidden. The other seven kinds of Treifos have permitted Sefekos, like we will explain.

Question: The Rambam did not explain himself. He almost contradicts what he wrote in Hilchos Ma'achalos Asuros, that "u'Vasar ba'Sadeh Treifah" includes all Treifos. The Ramach asked this. This is not so difficult. They are all included for lashes, but we are (more) stringent about Safek Drusah. However, it is proper to be stringent about whatever Moshe received on Sinai, even if it is not explicit in the Torah. If so, why is Drusah unlike other Treifos? We should be stringent about all of them! The Rambam agrees to this rule. He says that Kidushei Kesef is mid'Rabanan. He never brings an explicit source from the Torah for Kidushei Bi'ah. In many places, Perush ha'Mishnayos considers everything Moshe received like Torah law in every way. Regarding the other seven kinds of Treifos, why are we lenient about some Sefekos, and stringent about others? The Rambam agrees that we are lenient about some laws of Drusah involving a Safek, e.g. we are unsure whether it was cut by a reed or a cat.

Answer (Magid Mishneh): Indeed, we are stringent about anything Moshe received. There are four kinds of Safek. 1) An even Safek, i.e. there is no reason to favor one side over the other. We are stringent about this regarding any tradition from Sinai. Drusah is like other Treifos for this. 2) We know the Halachah, but we cannot see the case well enough. Also this we are stringent about in every case. 3) We are unsure if something occurred during its lifetime or after death. We are lenient regarding other Treifos. If possibly the hand punctured the lung after Shechitah, or a wolf punctured the innards, we assume so. Regarding Drusah we are stringent, e.g. a Dores entered a herd and we see a mark of Drisah on an ox' back. We do not say that it scratched itself on a wall. We are not so stringent about other Treifos. The Rambam is stringent when we see it Drusah in front of us, provided that the Dores came in front of us. This excludes when we are unsure if it was a dog or cat. Chachamim made this stringency, because Drusah is explicit in the Torah. It is not letter of the law.

Question: Letter of the law we should be stringent about Drusah, for the Chazakah is that a living animal is forbidden until we know that it was permitted (and a slaughtered animal is permitted until we know that it was forbidden)!

Answer (Magid Mishneh): Every animal is Muchzak to be healthy until we know that it was Nidras. The Chazakah that it is forbidden applies only to Ever Min ha'Chai or that it was not slaughtered. 4) We are unsure if it happened (that an animal scratched it), e.g. if a reed or cat scratched it. For this, we are lenient even about Drusah. This is unlike a lion that entered a herd. There, a Dores was Muchzak there. The only Safek is whether the wound is from the Dores. Regarding the reed, perhaps there was no Dores, and even if there was, perhaps the wound is from a reed. This is a Sefek-Sefeka, and the Torah us lenient about it. There is a proof for this from the Gemara.

Rivash (163): It seems that the Rambam is lenient about a Safek about a tradition from Sinai. The Ramban proved from Kidushin 39b that we are stringent it (unless there was a tradition to be lenient - Ramach). A tradition from Sinai can override an explicit Lav (Nazir 28b). The Perush of most of the Torah depends on traditions from Sinai. How can we say that it is like mid'Rabanan?! We are stringent about all Safek Treifos, unless there is reason to attribute (that it is Kosher), e.g. Chazakah or majority. This is why we check only the lungs, for lesions are common there, and even this is only l'Chatchilah.

Tosfos (43b DH ka'Savar): When there is a Safek, why don't we keep the animal in the Chazakah that it was not Drusah? Here is different, for Drisah is common.

Taz (YD 29:1): The Rambam means that we are lenient about a Sefek-Sefeka (two doubts) regarding other Treifos, but not for Drusah, unless we are unsure if a Dores was there. Alternatively, the Rambam answers Tosfos' question. Since Drusah is explicit in the Torah, we are stringent against Chezkas Heter.

Pleisi (50:1, b'Sof): We can say that among all the Treifos, the Torah chose to explicitly teach about Drusah because it is more common than the others. Therefore, we are stringent about a Safek.

Rambam (9:7): If all the skin was removed, it is Tereifah. If the width of a Sela remains along the entire spine and the navel and the joints, it is permitted. If the width of a Sela was removed from the entire spine or the navel or the joints and the rest of the skin is intact, it is a Safek. It seems that we permit it.

Rosh (3:47): R. Yanai's question was not resolved. We are stringent about a Safek mid'Oraisa. Ba'al ha'Itur says so. I do not know why the Rambam permits a Safek.

Kesef Mishneh: The Rambam holds that since each is in a particular place, it is a Safek, and we are Machshir (Vadai - PF) only if skin remains in all of the places. The Rashba and Ran agree. The Rashba and Rosh questioned the Rambam's final words, for it is a Torah Safek. I answer based on the Rambam in Perek 5, that we are lenient about Safek Treifos other than Drusah, for they are not explicit in the Torah. Also, since the Gemara did not resolve the question of skin removed from one of these three places, it is a Sefek-Sefeka. Perhaps the Halachah follows the Amora who disqualifies when skin does not remain there, and even if it does, perhaps he agrees when the skin was removed only from there, since the rest of the skin is intact. We are lenient about a Sefek-Sefeka.

Bach (29:3): The Beis Yosef understood that the Rambam is stringent whenever the Gemara was unsure about Safek Drusah, and lenient when it had a Safek about other Treifos. This is wrong. Rather, he is stringent about a Safek Drusah only regarding an even Safek. If there is more reason to forbid, he is stringent about all Treifos. If there is more reason to permit, he is lenient even about Drusah. He forbids Safek Drusah unless it is checked (5:11). Regarding a puncture, when possible we assume that it occurred after Shechitah.

Mishneh l'Melech (8:21): If a k'Zayis remained of the liver and it was spread out thinly, the Rambam (8:22) says 'it seems that it is forbidden.' We are stringent about every Safek Torah. (Surely it is forbidden!) He said similarly about a pressed skull. Regarding Gludah the Rambam is lenient about a Safek. If the brain softened, the Rambam said 'this is a Safek.' This is like he said, that regarding the other seven Treifos, we are lenient about some Sefekos. Therefore, when there is reason to favor the stringent opinion, he says 'it seems that it is forbidden.' When there is reason to favor the lenient opinion, he permits. Since they are not explicit in the Torah, they are somewhat like mid'Rabanan laws. When there is no reason to favor either opinion, he left it a Safek.

Poskim

Shulchan Aruch (YD 59:1): If all the skin was removed, it is Tereifah. If the width of a Sela remains along the entire spine and the navel and the joints, it is permitted. If the width of a Sela was removed from the entire spine or the navel or the joints and the rest of the skin is intact, it is Kosher.

Shach (2): The Rashba, R. Yerucham, Tur, Shiltei ha'Giborim, Maharshal and Bach forbid in the last case.

Question (Gra 2): The Kesef Mishneh's first answer is that the Rambam is lenient about Safek Tereifah other than Drusah. If so, what was the question why Ula is more lenient about a thorn stuck in the Veshet than about a Safek Nidras? Perhaps this is why the Rambam wrote that we are lenient about some Sefekos other than Drusah; he rules unlike Ula. This requires investigation.

Answer #1 (Bach 29:3): The Rambam says that we are stringent about a Safek Drusah only regarding an even Safek. The Gemara asked that surely we do not rely on Chezkas Heter regarding Safek Drusah because it is common, like Tosfos said. Likewise, a thorn often punctures the Veshet!

Answer #2 (Pleisi ibid.): Ula discussed a thorn in the Veshet, which makes a Neveilah, which is explicit in the Torah. Therefore, there is no reason why it should be more lenient than an explicit Tereifah (Drusah).

Rema: If skin was taken from all three places and the rest is intact, it is Tereifah.

Beis Yosef (DH v'Da): If the skin was removed from all three places (and the rest is intact), it is a single Safek, so it is Tereifah due to Safek.

Taz (1): Only when all three places are intact, they save and protect. The skin will grow back. If one of the three was removed and the rest is intact, it will not grow back and does not protect and save.

Hagahos ha'Taz: The Taz erased his Perush, and wrote 'if all three were removed, the skin will not grow back and what is there does not protect. If one of the three was removed, it will grow back, and protects and saves.

Gra (3): This question was not resolved, so we are stringent.