1) HALACHAH: AN ANIMAL'S ATTIRE AND "SHEMIRAH YESEIRAH"
OPINIONS: The Gemara records a Machlokes whether an item which provides excessive restraint or protection for an animal is considered attire (and the animal is permitted to go out with it on Shabbos) or a load (and the animal is not permitted to go out with it). What is the Halachah?
(a) The ROSH, RABEINU CHANANEL, RIF, and RAMBAM rule like Rav, who is stringent and says that any attire which provides extra protection is considered a load and is forbidden. They prove that the Halachah is like Rav from the fact that all of the Amora'im, who answer why the reins upon a Parah Adumah are not considered a load, apparently agree with Rav.
(b) The RA'AVAD cited by the RASHBA and RAN explains that in this case, we rule like Shmuel who is lenient, and one may let the animal go out with attire which provides extra protection. The reason the Halachah is like Shmuel is because we find that Rabah bar Rav Huna ruled like Shmuel (in the incident with Levi's donkey).
(c) The BA'AL HA'ME'OR (according to the RAN's understanding) says that in one respect, the Halachah is like Rav that an animal may not go out with an item that provides extra protection. However, the Halachah is also like Chananya and Rabah bar Rav Huna, who permit a cat to go out with a rope collar, even though it is considered extra protection. The reason for this is that a rope collar for a cat is the type of restraint that some people use all the time for their cats, and therefore it is not considered a load (even though it provides more protection than necessary). It was in such a case that Rabah bar Rav Huna permitted an animal to go out with extra protection.
HALACHAH: The SHULCHAN ARUCH (OC 305:17) rules that "Shemirah Yeseirah" is prohibited and a cow may not be taken out with a rope around its neck (like (a) above).
2) TURNING A MAN'S ORNAMENT INTO AN ANIMAL'S
QUESTION: RASHI (DH b'Va'in) explains that if one makes a man's ornament, such as a ring, into an ornament for an animal (such as a ring to fasten its collar), and it was Tamei before it was made into an animal's ornament, it retains its Tum'ah even when it is placed on the animal.
Rashi emphasizes that the ring was Tamei before it was put on the animal, because, apparently, after it becomes an animal's ornament it no longer can become Tamei. However, if this is true, then even if it is already Tamei it should lose its previous Tum'ah when it becomes an animal's ornament, because an animal's ornament cannot become Tamei! If, on the other hand, it can become Tamei even after it becomes an animal's ornament, then why does Rashi say that the ring was Tamei before it was put on the animal?
(a) TOSFOS (52a, DH b'Va'in) argues with Rashi and says that when a ring is made into an animal's ornament, it still can become Tamei. (It retains the status of an ornament of a man, since no physical change was made to it.) It indeed can become Tamei even when it is on the animal.
(b) The MAGINEI SHLOMO and PNEI YEHOSHUA defend Rashi's explanation. They write that the Gemara later concludes that the case under discussion is where one did make a physical change to the ring, but the change was a constructive one (i.e., it made the man's ring into a usable ring for an animal). In such a case, the Gemara explains, changing the ring physically does not cause it to become Tahor (according to Rebbi Yehudah).
RASHI understood that even according to Rebbi Yehudah, who says that a constructive change to the item does not make it Tahor, this only means that a constructive change cannot remove Tum'ah that was there already. However, a constructive change does prevent the item from being Mekabel Tum'ah in the future. (The ring, in this case, is now defined as an animal ring and not a man's ring, and an animal ring cannot become Tamei.)
Apparently, the reason for this distinction is that in order to make a Tamei item Tahor, one must break it, and a constructive change is not called "breaking" it. However, in order to prevent it from becoming Tamei, it is necessary only to give the item a new status. Even a constructive change gives an item a new status. Therefore, if a man's ring was made into an animal's ring, the ring cannot become Tamei once it has become an animal's ring. This is why Rashi says that the ring became Tamei before it was made into an animal's ornament. (Rashi's intention is to explain the Gemara in a manner consistent with the Gemara's conclusion.)
3) CORAL AND "TUM'AH"
QUESTION: The Gemara says that a ring made of "Almog" with a metal signet cannot become Tamei. RASHI says that the reason is because it is "Peshutei Kli Etz," a wooden item with no receptacle, which cannot become Tamei.
Why does Rashi have to say that it does not become Tamei because it is a "Peshutei Kli Etz"? "Almog," Rashi says, is "Atzei Almogim," which the Gemara (Rosh Hashanah 23a, Bava Basra 80b; see Rashbam, Bava Basra 81a) and the Bartenura (Kelim 13:6) define as coral. The Mishnah in Kelim (17:13) teaches that everything that grows in the sea is Tahor. The Rambam (Hilchos Kelim 1:3), citing the Toras Kohanim, writes that this refers not only to living creatures in the sea such as fish, but also to seaweed that grows in the sea. Coral should be no different from seaweed -- it should not be Mekabel Tum'ah because it grows in the sea! Why, then, does Rashi say that it is Tahor because it is a "Peshutei Kli Etz"?
(a) The TIFERES YISRAEL and SIDREI TAHAROS (Kelim 13:6) explain that the coral is attached to the earth at the bottom of the sea. Therefore, it is considered a tree and not an underwater organism, and thus the only reason why it is Tahor is because it is "Peshutei Kli Etz." The type of seaweed that is Tahor is a plant that grows while drifting in the water.
(b) The SIDREI TAHAROS cites an original explanation in the name of the YESHU'OS YISRAEL. The Mishnah in Kelim (17:13) states that if one attaches something that is Mekabel Tum'ah to an object that grew in the sea, the object that grew in the sea can now be Mekabel Tum'ah because of that attachment. Perhaps Rashi maintains that when one attaches something to the object that grew in the sea, the attachment turns the sea object into a regular land object, so to speak. Since the Gemara here is discussing a metal signet attached to a ring made of coral, the metal signet turns the coral into a land object, so that it can now be Mekabel Tum'ah. However, the coral does not become like the metal that is attached to it. Rather, it is considered like coral that grew on dry land, and it is grouped with wooden utensils. Therefore, it would have been Mekabel Tum'ah if not for the reason of "Peshutei Kli Etz." (The Sidrei Taharos, however, finds flaws in this reasoning.)