Question: If so, why can't we put the flank on top?

Answer: When handling the flank, the butcher breaks the membrane.

(Rav Yehudah citing Rav): A Chacham must train himself to do three things: signing his name, Shechitah and circumcision.

(Rav Chananya citing Rav): He must also know to make the knot of Tefilin, the blessing of Chasanim, and Tzitzis.

Rav Yehudah held that these are common, so a Chacham need not train himself to learn them.

(Rav Yehudah): Any butcher who does not know the laws of Shechitah, one may not eat from his Shechitah;

The laws (things which disqualify Shechitah) are: pausing; chopping the Simanim (not in a back and forth motion); inserting the knife between the Simanim and cutting; not completing the Shechitah in the ring of the windpipe in the Shechitah began; and uprooting one of the Simanim from its place.

Question: What is his Chidush? All of these are explicit in the Mishnah!

Answer: Even if we have seen the butcher slaughter nicely two or three times, we may not rely on his Shechitah;

Since he does not know the laws, perhaps he paused or chopped without realizing.

(Rav Yehudah): The butcher must check the Simanim after Shechitah.

Support (Rav Yosef - Beraisa - R. Shimon): If he paused the time needed for checking....

Suggestion: This is the time for checking the Simanim.

Rejection (Abaye): No, it is the time for the Chacham (of the city) to check the knife.

Objection: This time varies (depending how far away the Chacham is)!

Correction: Rather, it is the time for the butcher himself to check the knife (when he is the Chacham).

Question: If the Simanim were not checked, what is the law?

Answer #1 (R. Elazar ben Antigonus): It is like a Tereifah, and one may not eat.

Answer #2 (Beraisa): It is like a Neveilah, and it is Metamei one who moves it.

The two opinions argue about Rav Huna's law;

(Rav Huna): An animal is forbidden (to eat) when it is alive. After death, we assume that it is still forbidden unless we know that it was slaughtered properly;

If we know that it was slaughtered, we assume that it is permitted, unless we know what made it a Tereifah.

The Beraisa holds that we assume that it is still forbidden (it was not slaughtered properly), i.e. a Neveilah;

R. Elazar ben Antigonus holds that we know that it was forbidden to eat, so we assume it is still forbidden to eat; but we have no source to say that it is Metamei.

(Rav Huna): An animal is forbidden when it is alive. After death, we assume that it is still forbidden unless we know that it was slaughtered properly;

If we know that it was slaughtered, we assume that it is permitted, unless we know what made it a Tereifah

Question: Why didn't Rav Huna simply say 'if it was slaughtered, it is permitted (unless...)'?

Answer: He teaches that even if we have grounds to suspect that it was a Tereifah, we assume that it is Kosher.

Question (R. Aba): If a wolf took the innards of a slaughtered animal, what is the law?

Objection: If they are not here, what is the question?!

Correction: Rather - if it punctured the innards of a slaughtered animal, what is the law?

Objection: If we know that it punctured them, what is the question?!

Correction: Rather, if it took the innards of a slaughtered animal, and returned them punctured, what is the law?

Are we concerned that there was already a hole where the wolf bit?

Answer (Rav Huna): We are not concerned.

Question (Beraisa): If one saw a bird pecking at a fig, or a mouse making holes in a watermelon, we are concerned lest there was already a hole there (from a snake), and the food may not be eaten.

Answer (Rav Huna): You cannot ask from there. We are more stringent about danger than about prohibitions!

Question (Rava): What is the difference? In both cases, we are stringent about a Safek!

Answer (Abaye): We are not equally stringent!

We are lenient about a Safek of Tum'ah in Reshus ha'Rabim (a public domain). We are stringent about a Safek case of exposed water!

Rejection (Rava): Tum'ah in a Reshus ha'Rabim is an exception. It is a tradition from Moshe from Sinai, to learn from Sotah;

Regarding Sotah, we are stringent about a Safek only in a Reshus ha'Yachid (i.e. seclusion). Also for Tum'ah, we are stringent about a Safek only in a Reshus ha'Yachid.

Question (against Rava - Rav Simi - Mishnah): If a weasel was walking among loaves of Terumah, holding a dead rodent in its mouth, and we are unsure whether the rodent touched the loaves, we say that the loaves are Tahor.

In a Safek case of exposed water, we are stringent!

Answer: Also the case of the weasel is an exception. A tradition from Sinai teaches that we learn from Sotah;

We are stringent about Sotah, which is a case in which the party that became Safek Tamei (defiled, i.e. the woman) has understanding to answer questions. Also regarding Tum'ah, we are stringent only in such cases.

Question (against Rava - Rav Ashi - Beraisa): If a flask (with water to be sanctified with ashes of the red heifer) was left open and was found covered, it is Tamei. We assume that a Tamei person covered it;

If it was left covered and was found open, the water may not be sanctified with ashes of the red heifer if dew descended at night, or if a weasel can drink from it (i.e. it is not hanging in the air);

According to R. Gamliel, we are concerned even if a snake can drink from it.

(R. Yehoshua ben Levi): In the Reisha we are concerned for people. In the Seifa we are concerned for rodents, because it is the way of rodents to expose things, but not to cover them.

Regarding exposed water, we are concerned lest a snake drank from it (even if it was exposed from the beginning, and there is no evidence that anything happened at all)!