Gemara

Question (R. Chanina): If the animal stretches out its Kaneh by itself, is this Kosher for Shechitah?

45b - Question (R. Yirmeyah): If the spinal cord cannot stand due to its weight, what is the law?

46a (Mishnah): If k'Zayis of the liver remains, it is Kosher.

Questions (R. Yirmeyah): If the k'Zayis is not all in one place, what is the law? If it is stretched out in a strip, what is the law?

Question (Rav Ashi): If it is like a thin sheet, what is the law?

All these questions are unresolved.

Beitzah 3b (Beraisa): If an egg was laid on Shabbos or Yom Tov, it is forbidden. A Safek about such an egg is forbidden. If it became mixed with 1000, all are forbidden.

Question: Rav Yosef and Rav Yitzchak forbid the egg only mid'Rabanan. We should be lenient about a Safek mid'Rabanan!

Answer: The Beraisa forbids a Safek Tereifah egg.

Question (Seifa): If it became mixed with 1000, all are forbidden.

Granted, if it is forbidden due to Shabbos or Yom Tov, it is Yesh Lo Matirim (it can become permitted without Bitul, e.g. on a Yom Chol), therefore it is never Batel. However, a Tereifah egg should be Batel!

Answer: An egg is important, so it is not Batel. It is Davar sheb'Minyan (it is sold by number).

Zevachim 74a (Beraisa - R. Shimon ben Yehudah): If one forbidden pomegranate of Badan was mixed with 10,000, it forbids them. If one of them became mixed with three, and one of these became mixed, they are permitted.

Kesuvos 9a: If a Chasan claims that the Kalah was not a virgin, she should be permitted due a Sefek-Sefeka (two doubts)!

Perhaps the Bi'ah was before Kidushin;

Even if the Bi'ah was after Kidushin, perhaps she was raped.

Rishonim

Tosfos (3b DH v'Acheros): The Mishnah forbids even if the others became mixed with others, which is a Sefek-Sefeka. In Zevachim (74a), the Gemara struggled to find a Tana who holds like Shmuel, who forbids a Sefek-Sefeka. (This is based on Hagahos based on Chachmas Shlomo.) Why didn't it learn from here, that we do? Granted, above we can explain 'if it became mixed with 1000, all are forbidden' like R. Tam, that the Isur itself became mixed. Alternatively, above was a Beraisa, and it is no stronger than the Beraisa in Zevachim. To answer the Mishnah, R. Tam must say that the text does not say 'others became mixed in others.' The Ri says that the text says this. It means that also the Isur became mixed. One might have thought to permit, for this is like two majorities. Alternatively, we cannot learn from here, for an egg is important, therefore it is Batel only in two majorities. Here, the first Safek is not a majority. It is an even Safek.

Ran (Beitzah 13a DH Amar Shmuel): R. Asher of Lunil permitted Safek Muchan (perhaps it was not prepared before Yom Tov) on Yom Tov Sheni. Others disagreed. I approve. We permit Sefek-Sefeka even when Yesh Lo Matirim, since Yom Tov Sheni is a mere custom from our ancestors. We are not more stringent than they were. It was a Safek for them, so a Safek mid'Rabanan (Muktzeh) is permitted. Davar she'Yesh Lo Matirim is a stringency mid'Rabanan. Rav Ashi said so about a single Safek, but not regarding a Sefek-Sefeka. These are two Sefekos that can come only at once, so it is like a Yisrael's wife who was (perhaps) raped.

Teshuvas ha'Rid (71, to the Or Zaru'a, brought in Or Zaru'a 1:756:1): The Gemara (45a, 46a) left several questions unresolved. If pieces of such animals became mixed with others, are they Batel? Perhaps Eliyahu will come and be Machshir them, or Chachamim will find a reason to be Machshir, so it is Davar she'Yesh Lo Matirim! This is no reason not to be Batel. If he will be Machshir, it was never forbidden! The stringency of Yesh Lo Matirim is only when today it is clearly forbidden and tomorrow it is clearly permitted, like an egg laid on Yom Tov, or Chadash. Similarly, we do not disgrace Tevel or Hekdesh to be Mevatel them, since they are permitted through tithing or redemption.

Poskim

Shulchan Aruch (YD 110:9): If a Safek Tereifah became mixed with others, they are forbidden unless there is enough Heter to be Mevatel the Isur, if it is something that can become Batel. Since the first Safek is in the matter itself, we do not permit due to Sefek-Sefeka.

Beis Yosef (DH v'Ha): The Tur permits a Sefek-Sefeka only through a mixture. The Rashba said so in the name of the Ri. We permit only when both Sefekos come through mixtures, like the Gemara discussed a ring of idolatry that fell into 10,000, and one of those fell into 10,000. There are two Sefekos about each ring in the mixture. Perhaps it is not the ring that fell from the 10,000, and even if it is, perhaps it is not the initial Isur. When there are not two mixtures, we do not permit.

Beis Yosef (ibid.): The Rashba must explain Beitzah 3b to discuss the Safek. I.e. even if it is a Safek whether the egg was born on Yom Tov, if it became mixed, all are forbidden.

Suggestion: We should permit it, for perhaps it is not the Safek egg. And even if it is, perhaps it was not born on Yom Tov!

Rejection (Beis Yosef ibid., citing the Rashba): : We already forbade it by itself (before it became mixed). We cannot permit it afterwards. R. Tam says that the text does not say 'others in others', for every Sefek-Sefeka is permitted. The Yerushalmi supports this. Even so, one should be concerned for the Ri and permit only if both Sefekos are due to majorities. Therefore, if a Safek Tereifah became mixed with others, we permit due to Sefek-Sefeka only if the piece could have been Batel in a majority.

Beis Yosef (57 DH Kasav): Sefer ha'Mitzvos wavered about a Safek Drusah (perhaps it is Tereifah due to venom) that became mixed with others. He forbade. Semag cited the Ri, who says that a Beriyah (whole creation) or important matter is never Batel due to Safek or Sefek-Sefeka. Sefer ha'Terumah says the same about Chatichah ha'Re'uyah Lehiskaved (a nice portion proper to honor someone). If so, a Safek Tereifah mixed with 1000 forbids all of them, like Davar sheb'Minyan of a Vadai Isur, which is never Batel. However, if the Vadai Isur fell into two pieces of Heter, the Torah permits and Chachamim are stringent due to Davar sheb'Minyan. If one of them fell into a majority of Heter, all are permitted due to Sefek-Sefeka.

Rema: Some forbid because the Safek is an Isur Torah, so we cannot say that (perhaps) there is no Isur Torah. It merely became mixed with others, so this is not called Sefek-Sefeka, and it is forbidden. If there were two Sefekos if there is Isur here at all, and we found out about both together, we permit (such) a Sefek-Sefeka elsewhere, even for a Safek Torah and the Isur itself, even if there was Chezkas Isur. E.g. a bird had Chezkas Isur. If the wing broke or was dislocated, and perhaps this happened after Shechitah, and even if it was in its lifetime, perhaps the lung was not punctured, we permit due to Sefek-Sefeka. We need not check the lungs to clarify.

Beis Yosef (DH u'Motzasi): Some ask (Hagahos Tur ha'Shalem 27 - in Isur v'Heter of the Terumas ha'Deshen) how can the Ri argue with Zevachim 74, which permits Sefek-Sefeka? Also, if a Vadai Nidras became mixed in a majority, it is forbidden mid'Rabanan, so we should be lenient about a Safek (Nidras that became mixed)! I say that the Ri is stringent only when we know that a wolf clawed an animal before it became mixed. This is a Safek mid'Oraisa (whether its venom makes Tereifah), which becomes like Vadai Isur. When it became mixed, this is like a Vadai Isur mid'Oraisa mixed with Heter. If it was not known until it became mixed, also the Ri permits due to Sefek-Sefeka, since the Sefekos come together. Or Zaru'a and Semak connote like this.

Darchei Moshe (15, citing Isur v'Heter ha'Aruch 26:1): Our custom is to forbid any Sefek-Sefeka when the first Safek is mid'Oraisa, i.e. when there is a Vadai Isur mid'Oraisa, and another Safek was added from elsewhere. If there are two Sefekos whether there is an Isur mid'Oraisa at all, in one matter and in one item, we permit even regarding an Isur Torah. E.g. if a Yisrael finds that the Kalah is not a virgin, perhaps the Bi'ah was before Kidushin, and perhaps she was raped. We permit only when we learned about both Sefekos at once. Regarding a Safek Drusah, even if both Sefekos came at once, it is unlike other Sefek-Sefekos in the Gemara. Here, one Safek is whether there is an Isur Torah, and the other Safek is which animal in the mixture it is.

Darchei Moshe (DH Gam): The second question (in the Beis Yosef) is not difficult. A Safek about an important matter that is not Batel is not considered a a Safek mid'Rabanan. One should be stringent like the Ri even if both Sefekos became known at once.

Taz (12): The Ri permits only when both Sefekos are similar, both are due to mixtures, or both are whether there is an Isur. The Darchei Moshe and She'eris Yosef say so. I support them from the Rashba. He said 'the Gemara discusses an Isur that fell into two others, and one of them fell into two others. I.e. mid'Oraisa it is Batel in the majority. This implies that if it fell into only one of Heter, we would not permit due to Sefek-Sefeka. Perhaps when it falls into one of Heter, we consider both like the Isur itself because mid'Oraisa it is forbidden (due to Safek). Therefore, we are not lenient about a Sefek-Sefeka.' His latter answer is even according to R. Tam, even if one found out about both mixtures at once. Likewise, the first answer for the Ri is even if one found out about both at once. The Rashba brought both answers together, and did not distinguish.

Taz (13): Masas Binyamin (37 DH v'Od) wanted to prove from the Rashba that the Ri forbids only when the Sefekos came at different times, for we already forbade the first due to Safek. He relied on what the Beis Yosef cited from the Rashba. Really, the Rashba asked from the case of a Kalah, and answered that there the Sefekos always come together. When the Sefekos could occur at different times, we consider the first to be Vadai Isur, even if we did not find out until it became mixed. The Ran said 'these are two Sefekos that can come only at once, so it is like a Yisrael's wife who was raped.' Isur v'Heter similarly forbids Safek Drusah 'because the first Safek was (Asur) mid'Oraisa before it became mixed, i.e. when we will find out about it, so it became like a Vadai Isur.' He clearly forbids even if we did not find out in between. This applies whenever we forbid Sefek-Sefeka. Isur v'Heter explicitly says so later, but adds that when we permit, it is only when it became known in between. I disagree.

Shach (61): The Shulchan Aruch forbids when only one Safek was in the matter itself. This is like the Tur, Rashba and Poskim. However, they needed to say so because they permit a second mixture. The Shulchan Aruch (Sa'if 8) forbids two mixtures (and permits only three mixtures). Why did he need to say that only one Safek was in the matter itself? Also, why did he need to teach the law of Safek that became mixed? Why would one think that it is more lenient than two mixtures of any Isur? Why did the Rema need to say that the first Safek is mid'Oraisa? Do not say that they forbid even a double mixture of Safek Tereifah, for it is unlike three mixtures. Surely it is permitted due to Sefek-Sefeka. The Rema explicitly says so in Sa'if 8. This requires investigation.

Shach (62): The Mechaber forbids even when the first Safek is mid'Rabanan. Or, perhaps he agrees that a Safek mid'Rabanan is Batel in a majority.

Gra (37): The Rema is difficult. If we forbid when he found out in between, why did the Gemara (Beitzah 3b) struggle to explain why the mixture is forbidden? The Beraisa connotes that we found out, and then it became mixed!