1) ANNULLING A VOW WHEN THERE IS NO "CHACHAM"
QUESTION: Rav Chiya bar Amram (36b) teaches that three laymen may be Matir a Neder (rescind a vow) when there is no Chacham available. RASHI here (DH b'Makom) adds that when there is a Chacham, he may annul the Neder by himself.
Why does Rashi need to point out that a Chacham may annul the Neder by himself? This is implicit in the Gemara's statement!
ANSWER: REBBI SHLOMO EIGER explains that Rashi's intention is to prevent one from mistakenly interpreting Rav Chiya bar Amram's statement as implying that "when there is a Chacham, only he may annul the Neder" (as is the case when permitting a Bechor with a Mum). Rashi explains that three laymen may annul a Neder even when there is a Chacham in town, and Rav Chiya bar Amram means that a Chacham is the only one who can do it by himself.
2) FORBIDDEN FOOD THAT WAS INADVERTENTLY SOLD AND CONSUMED
QUESTION: The Mishnah states that if one buys and slaughters a Bechor and then discovers that it was never shown to a Mumcheh to determine that it possessed a Mum, the seller must return the buyer's money even though the buyer has already eaten the Bechor. Similarly, if one slaughtered a cow and sold the meat, and afterwards it was discovered that the cow was a Tereifah, the seller must return the buyer's money even if the meat has already been eaten.
RASHI (DH v'Yachzir) writes that the vendor must return the money he received for the sale of the Bechor because of a penalty imposed on him for selling something which might have been forbidden.
The NIMUKEI YOSEF in Bava Basra (46b of the pages of the Rif) states that when a butcher deliberately sells a Tereifah to a Yisrael, he is penalized and may not keep the money from the sale. The SHACH (YD 119:25) writes that according to the reason given by Rashi, this penalty applies only when it is clear that the seller knew that the food he sold was forbidden. If it is not clear that the seller knew that the food was forbidden, then he is not penalized, because perhaps he sold it inadvertently (b'Shogeg). The Shach states that this also appears to be the opinion of the Nimukei Yosef, who rules that the butcher is penalized only if he deliberately sold a forbidden item.
The ruling of the Nimukei Yosef and Shach seems difficult in light of the Gemara here. The Gemara cites a Beraisa in which the Tana Kama maintains that when one sells meat that is later discovered to be the meat of a Bechor, or fruit that is later discovered to be Tevel, or wine that is later discovered to be Yayin Nesech, even though it has already been consumed the seller must return the money to the buyer. Rebbi Shimon ben Elazar disagrees and distinguishes between a forbidden food to which a person is naturally repulsed, for which the vendor must return the money, and a forbidden food which is not naturally repulsive, for which the vendor does not need to return the money. RASHI (DH Yachzir) explains that since a person is repulsed by the food, he receives no benefit from it once he knows that it is forbidden. If it is not the type of food that is naturally repulsive to a person, then the vendor is not required to return the money, because the buyer still received benefit from the item. Things that are considered repulsive are Neveilos, Tereifos, and forbidden insects. In contrast, meat of a Bechor, fruit of Tevel, and forbidden wine are not considered repulsive.
From the fact that the Tana Kama mentions only food that is not considered repulsive when he says that the seller must return the money, it seems that he agrees with Rebbi Shimon ben Elazar that if repulsive food was sold, the vendor certainly must return the money. The Tana Kama and Rebbi Shimon ben Elazar mention only the other examples of forbidden food in order to demonstrate the strength of their opinion that even with non-repulsive Isur, the vendor must return the money. For non-repulsive Isur, the Tana Kama also penalizes the vendor, while Rebbi Shimon ben Elazar does not, since the customer derived benefit from the item.
Since everyone agrees that the factor that determines the vendor's obligation to return the money is whether the customer derived benefit, what difference does it make if the vendor knowingly sold the forbidden food or sold it inadvertently? Even if he sold it inadvertently, the vendor should be required to refund the money that he received in return for a repulsive forbidden item, because the customer derived no benefit from it! (Rashi writes that the refund is because of a penalty only as an explanation for why the money for the Bechor, which is not repulsive, must be returned. For Tereifos and other repulsive items, Rashi may agree that even if a penalty is not imposed in a case of Shogeg, the money still must be returned because the customer received no benefit.) (See MACHANEH EFRAIM, Hilchos Nizkei Mamon 9.)
ANSWER: The MAHARIT ALGAZI (#51) answers that whether the money needs to be returned because the customer received no benefit from the item depends on the nature of the repulsive item. He cites the TOSFOS CHITZONIYOS who asks why, according to Rebbi Shimon ben Elazar, is a Neveilah considered repulsive just because it was not slaughtered according to the Halachos of Shechitah, or why is a Tereifah considered repulsive if it is perfectly edible?
The Tosfos Chitzoniyos answers that, in fact, a Neveilah is considered repulsive to eat only when it died a natural death, and a Tereifah is considered repulsive only when it was torn apart by a wild animal (in the way that the Torah refers to a Tereifah; see Shemos 22:30). The RAMBAM (Hilchos Ma'achalos Asuros 4:7) writes that the Tereifah to which the Torah refers is an animal that was attacked by a wild beast of the forest and was mortally wounded by it, but has not yet died. Such an animal is fit only to be eaten by a dog, as the Torah states, "You shall cast it to the dogs" (Shemos 22:30). A person certainly is repulsed by such a Tereifah, but a person is not repulsed by an animal that is a Tereifah merely because it has one of the anatomical deficiencies which were taught to Moshe Rabeinu at Har Sinai.
Accordingly, the Mishnah refers to the type of Tereifah which does not repulse a person. Since he derives benefit from it, the vendor would not be required to return the money if not for the penalty imposed on him for knowingly selling something that is forbidden. It follows that if it was sold inadvertently, no penalty is imposed and the vendor may keep the money. However, if repulsive food was sold (such as an animal that died a natural death, or an animal that was torn apart by a wild beast), then even if the vendor sold it inadvertently, he must return the money to the buyer, since the buyer derived no benefit from the item. (D. BLOOM)
3) HOW IS NERO'S "SELA" THE EQUIVALENT OF A ROMAN "PUNDYON"
QUESTION: The Gemara quotes the Mishnah in Kelim (17:12) that states that an opening in a wall that was not made by man must be the size of a large fist in order for Tum'as Mes to pass to the other side. If the hole was made by man, then it must be the size of a hole made by a large drill (used in the Beis ha'Mikdash), which is the size of an Italian Pundyon coin, which is the size of a Sela of Nero (Niron), which is the size of the hole in an ordinary yoke.
How can a Pundyon be the same size as a Sela? The Gemara in Kidushin (12a) teaches that the value of a Pundyon is 1/48 of the size of a Sela!
ANSWER: The TIFERES YISRAEL (Kelim 17:12) explains that the Pundyon is made of copper, while the Sela is made of silver. Therefore, it is possible for their sizes to be the same while their values differ significantly.