(Beraisa #1): If one muzzles a cow that is Meraches (threshes grain that was soaked and dried) or threshes Terumah or Ma'aser, he does not transgress "Lo Sachsom" (Rashi - these were already Kevu'im for Ma'aser. Tosfos - Terumah and Ma'aser are not "Disho", i.e. food fit for it. Rambam - Meraches is stepping on grain while walking on its way. This is not considered work);

To avoid suspicion (others assume that it is regular Chulin), he brings a handful of the same species and hangs it near its mouth so it can eat.

R. Shimon says, he gives it vetch (horsebean), for this is the best food for it.

Contradiction (Beraisa #2): One who muzzles a cow that is Meraches does not transgress "Lo Sachsom." If it threshes Terumah or Ma'aser, he transgresses.

If a Nochri threshes with Reuven's muzzled cow, Reuven does not transgress;

If Reuven threshes with a muzzled cow of a Nochri, Reuven transgresses.

The Beraisos argue about Terumah and Ma'aser!

Answer #1 (regarding Terumah): He does not transgress if it threshes regular (mid'Oraisa) Terumah. He transgresses if it threshes Peros grown from Terumah seeds (which is only Terumah mid'Rabanan);

Question: The contradiction remains regarding Ma'aser!

Suggestion: Perhaps also regarding Ma'aser, he transgresses if it threshes Peros grown from Ma'aser.

Rejection: Granted, Peros grown from Terumah are Terumah, but Peros grown from Ma'aser are Chulin!

(Mishnah): Peros grown from Tevel or Ma'aser Sheni are Chulin.

Answer #1 (regarding Ma'aser): He transgresses if it threshes Ma'aser Rishon (it is like Chulin), but not if it threshes Ma'aser Sheni.

Answer #2 (regarding Ma'aser): In both Beraisos, it threshes Ma'aser Sheni;

Beraisa #1 is R. Meir, who says that Ma'aser Sheni is like Hekdesh. Beraisa #2 is R. Yehudah, who says that Ma'aser Sheni is like Chulin.

Question: In what case is it Ma'aser before threshing?

Answer: He declared it to be Ma'aser when it was still sheaves.

Question: According to R. Yehudah, why is he liable? He may not let the animal eat Ma'aser Sheni outside of Yerushalayim!

Answer: The case is, it threshes within Yerushalayim.

Answer #3 (regarding Ma'aser): He is liable for Ma'aser Sheni of Demai (doubtfully tithed Peros. Mid'Oraisa, they are Chulin.) He is exempt for proper (mid'Oraisa) Ma'aser Sheni.

This suggests another answer for Terumah!

Answer #2 (regarding Terumah): He is liable for Terumah of Demai, and exempt for proper Terumah.

Question: We find Ma'aser of Demai, but not Terumah of Demai!

(Beraisa): (Yochanan Kohen Gadol) instructed people not to say the declaration of Ma'aser (since it was enacted to give Ma'aser Rishon to Kohanim or the poor, people cannot say "Nesativ la'Levi"), and decreed that one who buys Peros from a commoner (i.e. one who did not accept all the stringencies of being trustworthy about Ma'aser) must separate Ma'asros;

This is because he found that many people separated only Terumah Gedolah, but not Ma'asros.

Answer #3 (regarding Terumah): He is liable for Terumas Ma'aser of Demai, and exempt for proper Terumas Ma'aser.

Question: If an animal was suffering diarrhea from eating, may he muzzle it?

If the Mitzvah is for the physical well-being of the animal, it is better that it not eat;

If the Mitzvah is because the animal is pained when it sees food and cannot eat it, he should let it eat!

Answer (Rav Sheshes - Beraisa - R. Shimon): He gives it vetch, for this is the best food for it.

This shows that the Mitzvah is for the physical well-being of the animal.

Question: May Reuven tell a Nochri 'muzzle my cow and thresh with it'?

One may not tell a Nochri to do Melachah on Shabbos. Perhaps this is a stringency of Shabbos (since one who desecrates Shabbos is liable to death), but it does not apply to muzzling, which is only a Lav;

Or, perhaps there is no distinction!

Answer #1 (Beraisa): If a Nochri threshes with Reuven's muzzled cow, Reuven does not transgress.

Inference: He does not transgress, but it is forbidden!

Rejection: Really, it is permitted. The Tana said 'he does not transgress' for parallel structure with the Seifa: if Reuven threshes with a muzzled cow of a Nochri, Reuven transgresses.

Answer #2 - Question (from Eretz Yisrael): If Nochrim steal bulls from Yisre'elim (their friends, who prefer castrated bulls for plowing), castrate them and return them, what is the law?

Answer (Shmuel's father): This is a ruse. We do not let the owners benefit from this; they must sell them. (Even though castration is only a Lav, one may not ask a Nochri to do it.)

Rejection (Rav Papa): In Eretz Yisrael, they hold like Rav Chidka, who holds that Nochrim are forbidden to castrate. If a Yisrael encourages them to do so, he transgresses "Lifnei Iver."

(Rava): Shmuel's father ruled that the bulls must be sold for slaughter.

Rejection (Abaye): It suffices that we fine the owner by forcing him to sell them.

Obviously, selling it to one's (adult) son is (permitted,) like selling it to a stranger.

Question: May he sell it to his minor son?

Answer #1 (Rav Achi): No.

Answer #2 (Rav Ashi): Yes.

Mereimar and Mar Zutra would exchange their bulls with each other (Tosfos - they did not want the Nochrim to castrate them. In any case, they did not keep them, lest people will suspect them).

Question #1 (Rami bar Chama): May one put a thorn in an animal's mouth so it cannot eat (while working)?

Objection: Surely not. That is muzzling!

Correction - Question #1 (Rami bar Chama): If an animal has a thorn in its mouth and cannot eat, must one remove it before working with it?

Question #2: May one set a lion near the animal, so it will be afraid to eat?

Objection: Surely not, that is muzzling!

Correction - Question #2: If a lion was near the animal, may one work with it? (Tosfos - even if one must remove a thorn, this does not show that one may not work with an animal that will not eat due to something not on the animal's body.)

Question #3: May one set the animal's child nearby, so it will be reluctant to eat? (Some texts - if the animal's child is nearby, what is the law?)

Question #4: May one put a hide over the grain, so the animal will not see what it threshes?

Answer (to Question #4 - Beraisa): Reuven may deny food to his cow in order that it will eat a lot when working by Shimon. One may put straw in front of his animal [on top of what it threshes] so it will not eat from what it threshes.

Rejection #1: There, it eats (straw, at least). If he puts a skin over, it will not eat anything.

Rejection #2: The Beraisa means that Reuven may put straw in front of his animal before it threshes, so it will not eat much when it threshes.

Question (R. Yonasan): If Reuven muzzled his animal before it started threshing, what is the law?

The Torah forbids muzzling when it threshes. He did not do this!

Or, perhaps it is forbidden to thresh with a muzzled animal?

Answer (R. Simai): (Kohanim may not drink wine) "b'Vo'achem." Does this forbid drinking only while in the Mikdash, but permit drinking beforehand?!

It says "u'Lehavdil" (he must be sober to distinguish)!

Rather, the verse teaches that at the time of coming, he may not be drunk;

Likewise, at the time of threshing, the animal may not be muzzled!

(Beraisa): If Reuven muzzled a cow or tied diverse species to a wagon and Shimon made them thresh or lead, Reuven is exempt and Shimon is liable.