1) NON-KOSHER ANIMALS THAT ARE CONSIDERED FOOD WITH REGARD TO "TUM'AS OCHLIN"
QUESTIONS: The Gemara cites the Mishnah in Uktzin (3:3) that states that the Neveilah of a non-Kosher animal in all places, and the Neveilah of a Kosher bird and Chelev in villages, require Machshavah in order to be able to become Tamei with Tum'as Ochlin, but they do not require Hechsher.
RASHI (DH Nivlas Behemah Teme'ah) explains that in all places one can assume that a Neveilah of a non-Kosher animal is not designated to be eaten because, besides being forbidden to Jews to eat, it is repulsive to Nochrim to eat. Therefore, it is not considered a food in itself until one gives it the status of food by having intention to eat it. Rashi writes that the Neveilah of a non-Kosher animal possesses two disqualifications from being considered food. The first is that it was not slaughtered according to Halachah. The second is that it is a non-Kosher animal and is forbidden to be eaten.
Rashi (b'Kefarim) explains that the reason why the Neveilah of a Kosher bird and Chelev in villages require Machshavah is that in those places the people are poor and are not accustomed to eating poultry and fats. Consequently, in those places poultry and Chelev are not considered food without Machshavah.
The Gemara continues and cites the rest of the Mishnah in Uktzin, which states that the Neveilah of a Kosher animal in all places, and the Neveilah of a Kosher bird and Chelev in "the markets" (Rashi explains that this refers to highly-populated cities where the people are wealthy and are accustomed to eating poultry and fats), do not require Machshavah or Hechsher. Rashi (DH Nivlas Behemah Tehorah) explains that the Neveilah of a Kosher animal has only one disqualifying feature: it was not slaughtered according to Halachah.
In the end of the Mishnah in Uktzin, Rebbi Shimon states that even a camel, hare, hyrax, and pig are considered food with regard to Tum'as Ochlin and do not require Machshavah or Hechsher. Rebbi Shimon explains that this is because they each have one of the Simanim of Kosher animals.
There are two basic questions on the Gemara here.
(a) Why is the Neveilah of a Kosher animal considered food? It can be eaten only when sold to a Nochri, but Nochrim prefer the meat of Chazir to the meat of a Kosher animal. Why, then, according to the Tana Kama is the Neveilah of a Kosher animal considered food more than pig?
(b) Why, according to Rebbi Shimon, does it make a difference that the camel, hare, hyrax, and pig possess one Siman of a Kosher animal? How does this fact make it more worthy of consumption and having the status of food? Just because it has one Siman does not make it more Kosher than an animal that has no Siman! How does having one Siman make it more of a food for Nochrim so that it does not require Machshavah to become Tamei with Tum'as Ochlin?
(a) TOSFOS (DH Nivlas Behemah Tehorah) writes that the relevant factor is not whether Nochrim want to eat the food, but rather how close it is to being permitted to a Jew. Accordingly, the Neveilah of a Kosher animal is considered food, because it if would not be a Neveilah, it would be fully permitted.
(b) The MELECHES SHLOMO (Uktzin 3:3, DH Af) answers that there is no choice but to say that, indeed, the decisive difference is whether the animal has two disqualifying factors or one. The Neveilah of a non-Kosher animal has two disqualifying factors. In contrast, an animal that has one Siman of a Kosher animal does not require Machshavah to become Tamei. (This is alluded to in the words of Tosfos.) (D. BLOOM)
2) "ISURO CHISHUVO"
QUESTION: The Gemara (9b) records a Machlokes between Rebbi Shimon and the Rabanan (9b) regarding whether a Peter Chamor (after Arifah) is subject to the laws of Tum'as Ochlin. The Gemara asks that since Rebbi Shimon permits one to benefit from a Peter Chamor after Arifah, it should be like any other food. Why does Rebbi Shimon say that it does not become Tamei with Tum'as Ochlin?
Rava explains that Rebbi Shimon and the Rabanan are discussing a Peter Chamor that was slaughtered with Shechitah by a Jew for practice. Both agree that there is no principle of "Isuro Chishuvo" -- the fact that the Torah prohibits eating it does not make it significant such that it can become Tamei with Tum'as Ochlin. Rather, they disagree about whether a non-Kosher animal that is slaughtered for practice is considered a food and is Metamei, just like a non-Kosher animal that a Jew slaughters for a Nochri.
Rava adds that the argument between Rebbi Shimon and the Rabanan is the same as the argument between Nimus and Rebbi Eliezer. However, the Gemara continues and explains that Nimus and Rebbi Eliezer argue about whether "Isuro Chishuvo"! How can Rava say that the argument between Rebbi Shimon and the Rabanan is the same as the argument between Nimus and Rebbi Eliezer, if he says that the former Tana'im are not arguing about "Isuro Chishuvo," while the latter Tana'im are arguing about "Isuro Chishuvo"?
ANSWER: RABEINU GERSHOM explains that although the Gemara -- when describing the argument between Nimus and Rebbi Eliezer -- uses the same term ("Isuro Chishuvo") that Rava uses earlier, the term here has an entirely different meaning. Rava uses the term to refer to an animal that was slaughtered for practice, and the word "Isuro" means "that which has been slaughtered not for eating, but for practice."