The Gemara rejects that possibility: Rav Naḥman is referring to the case of a new knife on which there is no residue.

The Gemara challenges: If it is a new knife, both according to Rabbi Yishmael and according to Rabbi Akiva, who disagreed about whether an idol is forbidden from the moment that one crafts it or from the moment that one worships it, a knife is merely in the category of accessories of idol worship, and accessories of idol worship are forbidden only after they are used for idol worship. The Gemara explains: If you wish, say that the reference is to a case where he cut a branch [gevaza] for idol worship with the knife, which leaves no residue. And if you wish, say instead that Rav Naḥman is referring to the case of an old knife that he burned until it became white hot in the fire, and therefore, there is no residue on the knife.

§ It was stated: With regard to one who slaughters an animal with the knife of gentiles, Rav says: He peels off a layer of the flesh from the place on the animal where the knife touched the flesh and the forbidden residue on the knife was absorbed. And Rabba bar bar Ḥana says: He rinses the place where the knife touched the flesh. The Gemara suggests: Let us say that they disagree about this, that one Sage, Rabba bar bar Ḥana, holds: The area of the slaughter on the throat is cold and does not absorb the forbidden residue, and therefore rinsing is sufficient. And one Sage, Rav, holds: The area of the slaughter on the throat is hot and therefore it absorbs the forbidden residue.

The Gemara rejects that suggestion: No, it is possible that everyone holds that the area of the slaughter on the throat is hot. For the one who says that he peels off a layer, it works out well, and the one who says that he rinses the place where the knife touched the flesh holds that since the two organs that must be severed in ritual slaughter [simanim], i.e., the windpipe and the gullet, are occupied with discharging blood, they do not absorb the residue.

There are those who say that everyone holds that the area of the slaughter on the throat is cold. For the one who says that he rinses the place where the knife touched the flesh, it works out well, and the one who says that he peels off a layer holds that although that area is cold, due to the pressure of the knife on the throat, the flesh absorbs the residue.

§ With regard to a knife with which an animal that is a tereifa was slaughtered, Rav Aḥa and Ravina disagree. One says: One purges it in hot water to remove the absorptions from the tereifa, and one says: One rinses it in cold water, and that is sufficient. And the halakha is: One may rinse it even in cold water. And if there is a tattered piece of a curtain with which to wipe the knife, one need not rinse it.

And according to the one who says that one purges it in hot water, what is the reason that he must do so; is it due to the premise that the knife absorbed forbidden residue? That reasoning should not be limited to a case where he slaughtered a tereifa. A knife with which he slaughtered an animal that is permitted should also require purging, because it absorbed residue from the limb from a living animal before the slaughter was completed. The Gemara answers: When is there concern that the knife absorbed the residue? It is when the throat grows warm. When does it grow warm? It is at the point when the slaughter is complete. At that moment, it is already permitted.

§ Rav Yehuda says that Rav says: The slaughterer requires three knives, one with which he slaughters the animal, and one with which he cuts meat, and one with which he cuts forbidden fats. One may not use the same knife for cutting the meat and the forbidden fats due to the residue on the knife after cutting the forbidden fats.

The Gemara suggests: And let him designate one knife for cutting both the meat and forbidden fats and cut meat with it and then cut forbidden fats with it. In this manner the forbidden residue on the knife will not affect the meat. The Gemara explains: The Sages issued a rabbinic decree prohibiting the use of one knife to cut meat and then forbidden fats lest he also cut forbidden fats and cut meat thereafter. The Gemara challenges: Now too, after the decree mandating separate knives there is a concern that they will be confused for him and he will use the knife that cut the forbidden fats to cut the meat. The Gemara explains: Since the Sages required him to have two knives, he has a conspicuous marker on one of the knives that will prevent confusion.

And Rav Yehuda says that Rav says: The slaughterer requires two vessels of water, one with which he rinses meat and one with which he rinses forbidden fats. The Gemara suggests: And let him designate one vessel and rinse meat with the water in the vessel and then rinse forbidden fats with the water in the same vessel. The Gemara explains: The Sages issued a rabbinic decree to prohibit doing so lest he rinse fats and rinse meat thereafter. The Gemara challenges: Now too, after the decree mandating separate vessels there is a concern that they will be confused for him and he will rinse meat in the vessel in which he rinsed fats. The Gemara answers: Since the Sages required him to have two vessels, he has a conspicuous marker on one of the vessels that will prevent confusion.

§ Ameimar says in the name of Rav Pappa: A person should not place [lisḥof] the flanks of an animal atop other meat so that the forbidden fats that are attached to the flanks are in contact with the other meat, due to the fact that the forbidden fat liquefies and flows and the meat absorbs it.

The Gemara raises an objection: If so, and that is a concern, when the flanks are placed in their typical manner [teritzi] as well, with the forbidden fat above the meat of the flanks, the forbidden fat flows and the meat of the flanks absorbs it. The Gemara explains: The membrane between the forbidden fat and the meat of the flanks interposes from below and prevents absorption of the forbidden fat. The Gemara challenges: If so,