Question: The two clauses of the Beraisa contradict each other!

Answer: The Shechitah is invalid when the knife was always attached. It is Kosher when the knife was originally detached and later attached.

(Beraisa): If one slaughters with a (knife on a) wheel, it is Kosher.

Contradiction (Beraisa): The Shechitah is invalid.

Answer #1: It is valid on a potter's wheel (since one makes it spin). It is invalid on a wheel turned by (flowing) water.

Answer #2: Both discuss a water wheel. It is Kosher if it was direct Ko'ach (the knife slaughtered right after a person released the water to start turning the wheel). It is invalid if it was secondary Ko'ach (it slaughtered later).

(Rav Papa): If Reuven tied up Shimon and directed water onto him, and this killed him, Reuven is liable for murder, for his action killed him.

This is only if his direct Ko'ach killed. If not, he only caused the death, and he is exempt.

(Rebbi): "He took the knife to slaughter" teaches that Shechitah requires a detached knife. (It said "took", which connotes something detached, and not "prepared".)

Question (Rav): How do we learn this from the verse?

Response (R. Chiya): Indeed, the verse does not teach like Rebbi says!

Question: If so, what does the verse teach?

Answer: It teaches the zealousness of Avraham. (He took a knife with him, lest he not find a rock Kosher for Shechitah.)

(Rava): If something was detached, and later attached, I am sure that it is considered detached regarding idolatry;

It was taught that if one worships his own house, it is forbidden.

If a house were considered attached, it would not become forbidden. "Their gods on the mountains" (are forbidden), but not the mountains (or anything else attached).

Regarding Hechsher (produce is Mekabel Tum'ah if one of the seven liquids was willingly detached and came on it), Tana'im argue about whether it is considered attached.

(Mishnah): If a man placed a bowl on a wall so that the bowl will get wet, and water fell on it, the water is Ki Yutan (it is Machshir any produce it touches);

If he placed a bowl so the wall will not get wet, water that falls on the bowl is not Ki Yutan.

Question: The Reisha teaches that if he wanted the bowl to get wet, the water is Ki Yutan. This implies that if he wanted the wall to get wet, the water is not Ki Yutan;

The Seifa says that if he didn't want the wall to get wet, the water is not Ki Yutan. This implies that if he wanted the wall to get wet, the water would be Ki Yutan!

Answer #1 (R. Elazar): We must say that different Tana'im taught the two clauses.

Answer #2 (Rav Papa): One Tana taught both. The Reisha discusses a wall of a cave (it was never detached, so it is considered attached). The Seifa discusses a wall that was built (the rocks were once detached, so it is considered detached);

The Mishnah teaches as follows. If he wanted the bowl to get wet, the water is Ki Yutan. This implies that if he wanted the wall to get wet, the water is not Ki Yutan;

This applies to a wall of a cave. Regarding a built wall, if he didn't want the wall to get wet, the water is not Ki Yutan. This implies that if he wanted the wall to get wet, the water would be Ki Yutan!

Question (Rava): If something was detached and then attached, may it be used for Shechitah?

Answer #1 (Beraisa): If a rock jutted out from the wall, or a reed grew on its own and one slaughtered with it, it is invalid.

Rejection: We cannot learn from there. The Beraisa discusses a wall of a cave. The rock was never detached.

Support: Presumably, this case resembles the case taught with it, a reed that grew on its own (and was never detached).

Answer #2 (Beraisa): If he stuck a knife in the wall and slaughtered, it is Kosher.

Rejection: There he will not leave the knife permanently in the wall. (Rava asked about something attached to be permanent.)

Answer #3 (Beraisa): If one slaughters with something attached to the ground, it is Kosher.

Rejection: Perhaps also this refers a knife. The above clause (Answer #2, which follows this clause in the Beraisa at the end of 15b), explains this clause;

(The Beraisa says) 'when is Shechitah with something attached to the ground Kosher? It is an attached knife, which is something that one does not leave in the wall.'

(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 pressed on the knife, and the Shechitah is invalid. (This is Derasah.)

Question: The Beraisa (15b, 3:f:1) permits, whether the knife is above the neck or below it!

Answer #1 (Rav Zvid): These apply in different cases;

If the knife is below and the neck is above, the knife must be detached;

If the knife is above and the neck is below, 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.

(Rav Chisda): Five laws were said about reeds:

They are not used to slaughter, nor to circumcise, nor to cut meat, nor to clean one's teeth, nor to clean oneself (after eliminating).

Question: Rav Chisda says that they are not used to slaughter, but a Beraisa permits Shechitah with anything, e.g. a rock, glass or reed!

Answer (Rav Papa): Only a Simona reed (a hard species) may be used.

We do not cut meat with reeds. Rav Papa would cut fish innards, for they are clear (if a chip falls off, it will be seen); Rabah bar Rav Huna would cut fowl, for it is soft (chips will not fall off).

Question: Why did he need to teach that one does not use reeds to clean oneself (after eliminating)? We already know this (from a more inclusive teaching)!

It was taught that if one cleans himself with something that burns easily, his (anal) teeth all out!

Answer: Rather, Rav Chisda meant that we do not clean a wound with reeds.

(Mishnah): All slaughter. We always slaughter.

'All slaughter' means that all is slaughtered, even fowl.

Question: Which Tana taught 'we always slaughter'?

Answer #1 (Rabah): It is R. Yishmael;

(Beraisa - R. Yishmael): "When Hash-m will widen your border... and you will say 'I want to eat meat'" permits Basar Ta'avah (animals that one desires to eat like Chulin, i.e. not a Shelamim).

In the Midbar, Basar Ta'avah was forbidden. When Yisrael entered Eretz Yisrael, it was permitted. After they were exiled, one might have thought that it is forbidden again. Therefore, the Mishnah teaches that we may slaughter even nowadays.

Question #1 (Rav Yosef): If so, why does the Mishnah say 'we always slaughter'? It should say, 'we always slaughter and eat'! (This is the Chidush.)

Question #2 (Rav Yosef): Initially, Basar Ta'avah was forbidden because Yisrael were close to the Mishkan (one who wanted to eat would bring a Shelamim);

Later, Basar Ta'avah was permitted because they were far from the Mishkan.

All the more so, in exile, one cannot bring a Korban, so Basar Ta'avah should be permitted! (There is no need to teach this.)