Gemara

(Mishnah): An animal Nidras (clawed and poisoned) by a wolf (is Tereifah).

(Rav): A (venomous) animal at least as large as a wolf is Matrif (makes Tereifah through Derisah) an animal.

Rav excludes what a cat is Dores.

Question: The Mishnah already teaches that a wolf is Matrif (i.e. but smaller animals are not!)

Suggestion: The Mishnah teaches that a wolf is Matrif even a large animal (but animals smaller than a wolf can be Matrif small animals.)

Rejection (Mishnah - R. Yehudah): A wolf is Matrif small animals. A lion is Matrif large animals (but a wolf is not);

(R. Binyamin bar Yefet): R. Yehudah explains the first Tana.

Answer #1: Rav argues with R. Binyamin. He holds that R. Yehudah argues with the first Tana. The first Tana holds that a wolf is Matrif even large animals!

Answer #2: Indeed, the Mishnah teaches a wolf to exclude a cat. Rav needed to teach this, lest we think that the Mishnah discusses a wolf because it is common.

(Rav Chisda): A cat is Matrif a kid or lamb.

Question (Beraisa): A cat is not Matrif, unless an interior organ was punctured. (If not, the venom will not kill it.)

Version #1 - Answer: Rav Chisda holds like Beribi;

(Beraisa - Beribi): A cat is Matrif only if someone saves its prey.

Question: Once, a cat chased a chicken. The chicken closed a door in front of the cat. The cat clawed the door. Blood exuded from all five claws. (This shows that it has venom!)

Answer: The chicken saved itself. This is like being saved by a person.

Chachamim agree that then it exudes venom. However, it is not Matrif.

Version #2 - Answer: The Beraisa is like Beribi.

Rav said that a cat is not Matrif large sheep, but it is Matrif kids and lambs.

Version #1 (Rav Kahana): A fox is not venomous.

Question: Rav Dimi reported that a fox was Dores a ewe, and Chachamim ruled that it is Tereifah!

Answer (Rav Safra): The case was, a cat was Dores it.

(Rav): We are not concerned about Safek cases of Derisah.

(Shmuel): We are concerned.

Both agree that we are not concerned in the following cases;

If we do not know whether a dog or cat clawed the victim, we assume that it was a dog;

If the attacker is sitting quietly among the herd, we assume that it made peace with them;

If the attacker cut off a head, we assume that this abated its rage, and it was not Dores any others.

If the attacker and the herd are both 'talking', we assume that both are afraid of each other. (It was not Dores.)

They argue when the attacker is quiet, and the herd is noisy. Shmuel holds that they are noisy because one was clawed. Rav holds that they are merely afraid.

(Ameimar): The Halachah is, we are concerned.

Rishonim

Rif (15b): A cat is not Dores adult small animals, but it is Dores kids and lambs, and all the more so birds.

Ran (15b DH Shu'al): Nowadays the custom is to permit chickens even if a cat entered the coop. Even though it would be proper to be concerned, we rely on the domestication of our cats. As long as we did not see that it hit, we are not concerned. If we saw that it hit, surely we are concerned!

Ran (16a DH Nach): If the attacker cut off a head, we are not concerned lest it was Dores others beforehand. Since its prey are in a place where it can be Dores any one it wants, we say that it was Dores and killed the first one (that it wanted to). This is only if it entered their place and stood among them. However, when cats come upon coops and stick their paws through the holes, even if it cut off a head, its anger did not subside. Since the birds flee, it gets angry. Also, only cutting off a head abates anger, but not being Dores. Whenever we are lenient here, we say that Vadai it was not Dores.

Rambam (Hilchos Shechitah 5:4): Even a cat is Dores kids and lambs, and all the more so birds.

Rosh (3:40): 'Alternatively, Rav excludes a cat' connotes that this is unlike the first answer. How do they argue? Also, what forced the Gemara to say that Rav argues with R. Binyamin? Perhaps Rav comes to explain the Mishnah, like R. Binyamin! A wolf is Dores only small animals, to exclude a cat. Rather, the Gemara suggested that a wolf is Dores even big animals, to teach that it is like a lion. It does not exclude a cat. Sefer ha'Terumah says that we are stringent like the version in which they (Chachamim and R. Yehudah) argue. The Rif disagrees. I hold like the Rif. We follow the version in which Tana'im and Amora'im do not argue. Also, the entire Sugya proves that cats are Dores lambs.

Rosh (ibid.): Rashi explains that Beribi distinguishes whether or not it was angry only regarding small animals and big birds. The venom can kill them only if it was amidst great anger. In any case it can kill small birds. In Version #2, Rav Chisda holds like Rabanan, that it is Matrif even if no one saved its prey. In Version #1, he holds like b'Ribi, that it is Matrif only if someone saved its prey. Presumably the Halachah follows Version #1. Even though Version #2 is more stringent, it is difficult to say that something is Dores small animals and small and big birds, but some (small birds) it kills in every case, and the others only if someone saved the prey. According to this ruling (like Version #1), we understand why people are not concerned if a cat entered a coop and it is quiet and they are noisy. Sefer ha'Terumah says so. However, the Rif does not distinguish between whether or not someone saved its prey. He is stringent like Version #2. We conclude that Rav holds that cats can be Dores small sheep.

Rashba (Toras ha'Bayis ha'Katzar 46, cited in Beis Yosef YD 57 DH u'Mah): Often, cats enter where the chickens are, and we are not concerned. Some explain that this is because cats are Dores only when one saves its prey. This is wrong. Perhaps it is because our cats are domesticated (and live) with chickens, so if we did not see it chase them v'Hikah (and or hit), we are not concerned. It is proper to be concerned.

Beis Yosef (YD 57 DH u'Mah): The Rashba says that it is proper to be concerned because in the Gemara they were concerned. Their cats were regularly around chickens just like our cats.

Poskim

Shulchan Aruch (YD 57:5): Some say that nowadays the custom is to permit chickens even if a cat entered the coop. Even though it would be proper to be concerned, we rely on that our cats are domesticated, so if it did not hit it, we are not concerned.

Bach (11): Regarding venomous animals, the Tur does not distinguish whether or not someone saved the prey. This is like Version #2, which is stringent. Sefer ha'Terumah rules like Version #1, which is lenient about a cat when no one saved its prey and the prey did not save itself. Then it is not angry, and it does not cast venom. We are lenient only when the cat entered the coop, i.e. there is no one to save, but when there is a closed coop with holes in the wall, and cats that stick their paws through the holes, the birds save themselves. They flee in the coop itself from corner to corner. The cat gets angry and is Dores, even according to Sefer ha'Terumah. The Ran and Isur v'Heter explicitly say so.

Taz (9): The Shulchan Aruch discusses when the cat is quiet and the chickens scream. If not, we are not concerned even for venomous animals (Sa'if 9). The Shulchan Aruch connotes that if we saw that it hit, we are concerned. This is even if all are quiet, for in Sa'if 11 he forbids if we saw it jump upon them like Dorsim, even if all are quiet, even if it is domesticated. The same applies here when it Vadai hit it. The Tur and Rashba say 'as long as we did not see it chase after them v'Hikah', which connotes that it chased and hit. We are not concerned if we saw it do only one of these. The Shulchan Aruch wrote only 'we did not see it hit.' This is from the Ran. I.e. if we only saw it hit, we are concerned. If the Shulchan Aruch understood that the Rashba forbids if it chased or hit, he should have mentioned also chasing, and teach that we are concerned for either of these by itself. It is difficult to say that the Ran and Rashba argue. Rather, every case of hitting is through some chasing. The victim always wants to save itself, so the aggressor must chase it a little. If was not in the way of hitting, rather, they were standing next to each other and it put its hand on it, surely this was mere playing.

Bach (DH ul'Inyan): The Shulchan Aruch connotes that if it surely hit it, we are concerned. This is when the cat is quiet and the chickens scream. Therefore, if our cats were not domesticated, we would be concerned even if it did not hit. However, the Rashba connotes that we are concerned only if it chased and hit. This is when both are quiet, so we are not concerned for hitting alone. In any case it is proper not to eat them. The same applies when it entered the coop and it is quiet and they are noisy. In these two cases one may sell them to Nochrim, for letter of the law they are permitted. When both are quiet and we did not see it hit, one need not be concerned at all. Hitting is only amidst anger, e.g. amidst chasing it. However, when both are quiet, cats often hit chickens and we are not concerned. We assume that it was like playing. However, it is proper to be concerned even if it did not chase it, or if it entered the coop and it is quiet and they are noisy.

Taz (9): I say that even if it is quiet and they are noisy, we are not concerned if we did not see it hit. Even though they are afraid, since our cats are domesticated, we are not concerned. The Rashba and Ran explicitly permitted this based on letter of the law. We should be stringent only if we saw it hit while chasing, even if both are quiet. One may sell it to Nochrim due to a Sefek-Sefeka (two doubts). Perhaps he will not resell it to a Yisrael. Even if he does, perhaps it hit only in play. Even though the Poskim are stringent when it hit, it is not a Vadai Isur. It is a mere concern. Those who are stringent to kill them first (so surely no Yisrael will buy it from the Nochri) will be blessed.

Shach (18): There is no need to say like the Bach. There is no question against the Shulchan Aruch. He says that when it did not hit, we are not concerned. If we saw it merely hit, we are concerned, like in Sa'if 11. Perhaps one may sell them to Nochrim. Sefer ha'Terumah, Isur v'Heter and other Poskim permit when no one saved its prey. Even though we do not rule like them, perhaps we may rely on them to sell them to Nochrim due to Sefek-Sefeka.

Gra (21): It seems that one may be lenient about big (chickens). Even though Drisah applies, it is not usual. This is like we say in Bava Kama (15b, that it is unusual for cats to eat chickens). The Rosh (3:40) says that even though dogs normally eat Neveilos of large animals, they do not normally kill them, therefore we are not concerned.

Shulchan Aruch (11): When both are quiet, we permit only if we did not see it hit them. If we saw it jump upon them like Dorsim, even if it is domesticated, it is forbidden.