(Abaye and Rava): If one slaughtered Kodshim Kalim while they were hanging (in the air), it is Kosher.

Shabbos 128b (Abaye): If one slaughters a hen, he should bend its feet against the ground or lift it totally off the ground.

Chulin 16b (Beraisa): If one stuck a knife in the wall and slaughtered, it is Kosher.

(Rav Anan): This is only if the knife was above the neck. If the knife was below the neck, we are concerned lest the neck will press on the knife, and the Shechitah is invalid (this is Drasah).

Question: The Beraisa (15b) permits whether the knife is attached or detached, whether it is above or below!

Answer #1 (Rav Zvid): If the knife is below and the neck is above, the knife must be detached. If the knife is above, the knife can even be attached.

Answer #2 (Rav Papa): The Beraisa discusses a bird, which is light. There is no concern lest its neck press.

Rambam (Hilchos Shechitah 2:7): How does one slaughter? He stretches the neck, and moves the knife back and forth until he slaughters. The animal crouches, or stands and he holds the back of the neck and the knife is in his hand below. This is Kosher.

Rosh (Chulin 1:23): Rav Anan did not say 'lest the neck pressed on the knife.' Rather, he used the future tense 'lest the neck will press', to teach that even if he says 'I am sure that I did not press', it is Pasul, lest another time he will press. Therefore, if it was a bird, whether the neck was above or below the inserted knife, the Shechitah is Kosher.

Ran (Chulin 4b DH li'Tzdadin): Rav Zvid answered that when the knife is below, it must be detached. He moves the knife back and forth. Rav Papa holds that this is a poor answer. Rather, the Beraisa discusses a bird. It is light, so there is no concern lest its neck press.

Shulchan Aruch (YD 6:4): If a knife was inserted in the wall (Rema - or in something detached) and one passed the neck along it until he slaughtered, it is Kosher. This is when the neck is below and the knife is above. If the neck was above, perhaps the animal would descend due to its body weight and cut without going back and forth, and this is not Shechitah. Even if he is sure that he did not press, it is Pasul. Therefore, if it was a bird, whether the neck was above or below the inserted knife, the Shechitah is Kosher.

Beis Yosef (DH v'Ha): Rav Zvid and Rav Papa do not argue about the Halachah. They argue only about how to establish the Beraisa. This is why the Rif, Rambam and Rosh rule like both of them.

Shach (8): Why did the Rema need to say 'or in something detached'? All the more so it is Kosher! The Chidush is in the Seifa. When the neck is above, it is Pasul even if the knife was inserted in something detached. Alternatively, he teaches that when the neck is below, it is b'Di'eved even if the knife was inserted in something detached. It is clear from the Gemara that when the knife is detached, when the neck is above it is Kosher b'Di'eved. Even for a bird, l'Chatchilah the neck may not be on top.

Rebuttal (Pri Chodosh 11): The Gemara proves unlike the Shach's latter answer. When there is no concern for Drasah, it is l'Chatchilah.

Meshiv Davar: A Tosefta (Chulin 1:2) explicitly permits Shechitah with a detached or attached knife, whether the neck is above or below. The Shach holds that just like this is not the Halachah regarding an attached knife, also regarding when the neck is above. This is wrong.

Gra: The Rema teaches that when the neck of the animal is above, it is Pasul even if the knife was inserted in something detached. When the neck of an animal or bird is below, it is l'Chatchilah even if the knife was inserted in something detached.

Beis Yosef (DH u'Mah she'Chosav Rabeinu): The Rashba says that presumably we are not lenient about all birds, rather, only for light birds such as chickens or lighter. For a goose or heavier, we are concerned lest they weigh down like an animal. The Tur says that since the Gemara did not distinguish between different birds, all are permitted. We can say that since birds are permitted because they are light, it is understood that if it is heavy we are concerned. Also, perhaps 'Ohf d'Kalil' means 'a bird that is light', and it excludes heavy birds. The simple reading of the Gemara is 'a bird, which is light', like the Tur.

Beis Yosef (DH v'Chasuv): The Kolbo says that some say that the neck of lambs is light, like of birds, so they are similarly permitted. There is no source for this. The Rashba wanted to forbid heavy birds such as geese, and all the more so lambs! The Tur equates all birds to permit them, and similarly equates all animals to forbid them.

Tosefes Merubah (in Otzar Meforshim in Shulchan Aruch ha'Shalem, citing Simlah Chadashah 9 and Tevu'os Shor 16): Chayah is included in Behemah, even though some of them are naturally light. (Note: there are seven Kosher Chayos (Devarim 14:5). Amora'im were unsure about the identity of some of them (Chulin 80a). Among those known (deer, hart) and what I have seen suggested (wild ox, giraffe...), none of them are lighter than geese.)

Shulchan Aruch (24:20): One who slaughters a chicken must be careful to press its legs into the ground or hold it up, lest it insert its feet in the ground and the Simanim will be uprooted.

Tosefes Merubah (in Otzar Meforshim in Shulchan Aruch ha'Shalem): Tevu'os Shor (36) says that the Shulchan Aruch refers only to a rooster, but Yam Shel Shlomo (2:16) connotes that the text is hen, and this is the text in Shabbos.

Aruch ha'Shulchan (49): When a chicken is stood up on the ground or against a wall with room, and one wants to slaughter it, its nature is to dig its nails into the ground and uproot the Simanim. If one presses the legs into the ground or wall or suspends it in the air, it is unlikely that they will be uprooted. Therefore, Chachamim commanded to do so.

Har Tzvi (YD 11): In a certain city they used to hang the animal from its legs above with the neck below, and slaughter from the side. The society for prevention of cruelty to animals says that this is painful. They want the animal to hang on ropes under its stomach in an upright standing position with the neck up, and the Shochet will slaughter from below. The Rambam (2:7) said 'how does one slaughter?' This connotes that this is l'Chatchilah if it stands and the knife is under the neck. However, the Shach says that it is clear from the Gemara and Poskim than l'Chatchilah one may not slaughter when the knife is below. The Pri Chodosh said that this is unlike the Gemara. The Pleisi says that only when one moves the neck along the knife there is concern for Drasah, but when one moves the knife this is called that the knife is above and even the Shach permits in every case. If so, why did the Pri Chodosh argue with the Shach? Rashi explains that he moves the knife, in which case also the Shach permits! Tevu'os Shor says that Rashi permits a suspended animal only if the neck is tied so it cannot weigh down. Simlah Chadashah (8) permits when the neck is above only if the head is tied.

Note: The end of the Teshuvah was lost. Igros Moshe holds like the Pleisi, and says that therefore there is no question against the Shach.

Har Tzvi (YD 14): In Argentina, they slaughter big bulls when the neck is pressed against a beam and the body is suspended in the air. This is Pasul. Perhaps the body will weigh down and uproot the Simanim. There is no proof from Zevachim to permit. Perhaps the animal is suspended by its legs, or rests on something hanging in the air. Minchas ha'Zevach forbids those who slaughter geese while holding it only by the neck and the body hangs down. This is Pasul, for it weighs down and the Simanim tear. Simlah Chadashah (24:25) requires someone else to hold the Simanim with the Shochet, lest they move.

Si'ach Yitzchak (390): Pekudas Eliezer (66) says that the animal must lie on the ground, tied, and the Shochet holds it and the knife, so it cannot lift its neck and weigh down on the knife. If it hangs on wood, even if people hold the head, perhaps it will overpower them for a moment and press down. When it is hanging and the knife is above, it must be tied so it cannot lift its neck. In the Mikdash, there were rings in which the animal's neck was inserted (Rashi Sukah 56a DH v'Tabasah), so it not move at the time of Shechitah (Tiferes Yisrael 75).

Igros Moshe (YD 2:13): Rashi (Chulin 16b DH Sachin) explicitly says that it is l'Chatchilah to slaughter through moving a detached knife when the animal is suspended and the neck is above. The Shulchan Aruch forbids with a detached knife, and the Shach forbids l'Chatchilah when he moves the animal's neck along the knife. He learned from Rashi, who permits l'Chatchilah when one moves the knife back and forth. B'Di'eved it is Kosher even if he moved the neck. This is unlike Simlah Chadashah, who forbids even b'Di'eved. We do not find anyone who disagrees with Rashi. Nekudas ha'Kesef says that Tosfos agrees. Rashi connotes that the head need not be tied, for he did not mention this. When it stands normally on the ground it has power to press down its neck, but not when it is hanging. Perhaps this is a Heter for the practice in Argentina, but l'Ma'aseh I do not permit, for it seems that Simlah Chadashah forbids even when it is hanging. It is permitted only if the head is tied above, like Tevu'os Shor permits.