On a De'oraita (Biblical) level, there is an Isur (prohibition) to shear the wool of a Bechor (firstborn animal). The Pasuk (verse) tells us, “Don’t shear the wool of your Bechor.” This Isur even applies to a blemished Bechor. But that is all talking about shearing with a utensil—the proper utensil used for shearing. If a person plucks hair by hand, on a Biblical De'oraita level, it is permitted. But the Hachamim (Sages) added a safeguard and said that tearing an animal’s wool by hand is prohibited as well. It is Derabanan (rabbinic). Here we’ll talk about exceptions to that Derabanan rule.
The Mishnah says, Rabbi Yosei ben Meshulam says, “Ha-tabach oseh makom ba-kofitz mikan umikan, vetolesh et hase'ar.” Someone who is slaughtering a Bechor, whether we’re talking about an unblemished Bechor that he’s bringing as a Korban (offering), or a blemished Bechor that he’s bringing outside the Beit HaMikdash, is allowed to make space for the slaughtering knife, the meat cleaver, to either side by pulling out the hair on the neck. So he is allowed to show the spot where the Shechita (slaughtering) is going to be. He is allowed to rip out the hair by hand, even though that is usually Assur Midrabanan (prohibited), as long as he doesn’t move the hair from its place. After plucking the hair, he has to leave it entangled in the hair that remains on either side. If he removes the hair from the neck, people may think that he is shearing an animal that was already dedicated, which is forbidden. So what he has to do is leave the detached hair dangling on either side of the cleared space. By leaving the wool on the animal, he is showing why he is plucking out the hair. He is doing it not to use the wool, but to make a space there so he can see where he is doing the Shechita.
A blemished Bechor is not brought as a Korban; rather, it is slaughtered and eaten. There’s no idea of redemption either. But it first has to be checked by a Hacham, who can determine that the blemish is the type that would exempt it from the proper slaughter in the Beit HaMikdash. Here we’ll talk about the previous law and how it applies in this situation. It is the same law as in the last part of the Mishnah: if somebody wants to pull out the hair of the Bechor that has a possible blemish and is bringing it to be examined by a Hacham, and the animal’s hair is covering up the spot of the blemish, he is allowed to pluck out the hair and let the Hacham inspect, as long as, likewise over here, he leaves the hair entangled in the surrounding hair, which shows he is not planning on using it for any other purpose.