GEMARA: The mishna teaches that an agent is considered to have diverged from the instructions of the homeowner if he gives each of the guests liver instead of meat or vice versa. This indicates that meat and liver are considered two different types of items, as giving one in place of the other would normally be done only after consultation with the homeowner. The Gemara asks: Who is the tanna who taught this halakha, that any case involving an item about which the agent would normally consult whether to give it or to give another item in its stead is considered to involve two separate items with regard to the prohibition of misuse?

Rav Ḥisda said that this is not in accordance with the opinion of Rabbi Akiva. As we learned in a mishna (Nedarim 54a): In the case of one who takes a vow that vegetables are prohibited to him, without specifying which types of vegetable, he is permitted to eat gourds, as people do not typically include gourds in the category of vegetables; but Rabbi Akiva deems it prohibited for him to eat gourds. Rabbi Akiva maintains that as an agent would consult the homeowner before buying gourds instead of vegetables, they are in the same category. He reasons that if they were not both in the same category, the agent would not even bother consulting the homeowner if he would prefer gourds instead. Therefore, Rabbi Akiva maintains that any item about which the agent would ask is included in the same category as the item he specified, and they are not two separate items.

Abaye said: You may even say that the mishna is in accordance with the opinion of Rabbi Akiva, as doesn’t Rabbi Akiva concede that the agent needs to consult the one who appointed him? Since the agent failed to consult him, and he acted on his own when he gave liver instead of meat, he is not considered to have performed his agency. Consequently, he is liable for misuse. In other words, the ruling of the mishna is not due to the fact that meat and liver are considered two different types of items, but because the agent failed to perform his agency. When the Rabbis said this halakha before Rava, he said to them: Naḥmani, i.e., Abaye, is saying well.

The Gemara asks: Who is the tanna who disagrees with the opinion of Rabbi Akiva in the mishna in tractate Nedarim? The Gemara answers that it is Rabban Shimon ben Gamliel, as it is taught in a baraita: With regard to one who takes a vow that meat is forbidden to him, he is prohibited from eating all types of meat, and is prohibited from eating meat of the head, of the feet, of the windpipe, of the liver, and of the heart, despite the fact that people do not typically eat meat from those parts of the body. And it is prohibited for him to eat meat of birds, as that too is popularly called meat. But it is permitted for him to eat the meat of fish and grasshoppers, as their flesh is not called meat. Rabban Shimon ben Gamliel permits him to eat meat of the head, of the feet, of the windpipe, of the liver, of the heart, of birds, and needless to say also of fish and of grasshoppers.

And Rabban Shimon ben Gamliel would likewise say: Innards are not considered meat, and one who eats them is not a person, i.e., innards are unfit for human consumption. It can be inferred from here that Rabban Shimon ben Gamliel disagrees with Rabbi Akiva and maintains that although an agent who fails to find meat would consult the one who appointed him and then replace the meat with liver, the liver is not considered meat with regard to vows.

With regard to the above baraita, the Gemara asks: And according to the opinion of the first tanna, what is different about meat of birds that he considers it in the same category as regular meat? It must be because a person normally says, when he cannot find meat and returns to the one who appointed him: I did not find meat of animals but I brought meat of birds instead. The Gemara asks: If so, then also with regard to fish a person is apt to say: I did not find meat of an animal, but I brought fish instead. Why, then, is fish considered a separate category?

Rav Pappa said: We are dealing with the day of one’s bloodletting, as a person in that condition does not eat fish. Since it was accepted at the time that eating fish after bloodletting is harmful, the agent would never consider buying fish instead of meat, and would not even consult with the one who appointed him as to whether or not to purchase fish.

The Gemara asks: If so, he would not eat birds either, as Shmuel said: With regard to one who lets blood and eats the meat of a bird, his heart rate accelerates and flies like a bird. Clearly, bird meat is also deleterious for one’s health after bloodletting. And furthermore it is taught in a baraita: One does not let blood before eating fish, nor before eating birds, nor before eating salted meat.

Rather, Rav Pappa said: We are dealing with a case which occurred on a day that his eyes hurt him, as people do not eat fish on that day, since fish are harmful to the eyes. Therefore, the agent would neither purchase fish nor consult with the homeowner whether to do so.

§ The mishna teaches: If the homeowner said to the agent: Give him meat, a piece for each guest, and the agent says: Each of you take two pieces, and each of the guests took three pieces, all of them are liable for misuse. The Gemara suggests: One can learn from the mishna that if an agent adds to his agency he is still considered an agent, and therefore the one who appointed him is also liable, as the agent did not uproot his instructions entirely.

Rav Sheshet said that this inference is not necessarily correct, because the mishna can be explained as referring specifically to a case where the agent said to the guests: Take one piece of meat in accordance with the intent of the homeowner and one piece in accordance with my intent.