Explanation #1 (Rashi): These are teeth [of a lock] of bone. One puts them in a lock, in order to open [it via a key]. Before they are fixed [in a lock], they have no use;

After he fixed them in a lock they are Temei'im, for bone Kelim are like metal Kelim. [Even] Pashut Kelim [of metal, which have no interior] are Temei'im, like it says in Chulin (25b).

Implied question: They are attached to the [wooden] lock, and what is attached to something Tahor is Tahor! (A Pashut wooden Kli is Tahor.)

Answer: A lock has a receptacle. It holds the key.

Objection #1: [Rashi] explained that Pashut bone Kelim are Temei'im, like it says in Chulin (25b). He was not precise;

There it discusses only unfinished bone Kelim, but Pashut bone Kelim, a Mishnah brought above (16b) teaches that Kelim of wood, leather, bone or glass, if they are Pashut, they are Tehorim!

Objection #2 (Ri): [Rashi] explained that the teeth are of bone. This was taught regarding metal Kelim in the Tosefta in Kelim (Bava Metzi'a 3:7)!

Objection #3: If before they are fixed [in a lock], they have no use, obviously they are Tehorim!

Objection #4: [Rashi] explained that a lock has a receptacle to hold the key. This is not considered a receptacle, for the key is not wont to be moved through the receptacle!

This is like an amputee who may go out with his false foot; it is Tahor when there is no receptacle for tufts. Rashi explained that [even though] he puts the end of his leg into it, it is not considered a receptacle, for the leg is not moved through it.

Objection #5: [Rashi] explained that the lock causes Tum'ah to the teeth. Just the contrary, a Mishnah in Kelim (13:6) teaches that if a wooden lock has metal teeth, it is Tamei. If a metal lock has wooden teeth, it is Tahor. This shows that the law depends on the teeth! (It is considered a Pashut wood or metal Kli based on its teeth.)

Implied question: It connotes that it is like R. Nechemyah, who does not follow the law of the Ma'amid (what holds something in place), rather, the law of what is used, i.e. the stamp (and not the ring that holds it. However, Chachamim follow the law of the Ma'amid!)

Answer (Ri): Also the Beraisa in our Sugya is like [R. Nechemyah], for the Seifa (Tosefta 3:8) teaches here that a metal ring with a balsam stamp, R. Nechemyah is Metaher!

Explanation #2 (Ri): The teeth are of metal. Even if they were not fixed [in a lock], they are somewhat proper to put them in a lock (to open it, as if it were a key), and even so, they are Tehorim, for unfinished metal Kelim are Tehorim;

If he fixed them in a lock, their work (preparation) is finished.

Support: It connotes like this below, that the reason is due to being finished, for it teaches "of a door, even though they were fixed in the door..." It connotes that fixing them in the door should cause Tum'ah, since there is no lock (therefore it is finished), but since it is fixed in the door, it is Tahor (since it is attached to the ground).

Explanation (Rashi): One who needs to defecate, and he cannot, it is forbidden to use a rock [to open the anus to enable the excrement to leave], because this uproots hairs.

Question: Regarding Davar she'Eino Miskaven, Rava holds like R. Shimon [who permits], in Beitzah (23a)! The Gemara asks like this below against R. Yochanan, who forbids due to uprooting hairs.

Answer: Here that he uses a rock, it is a Pesik Reishei [that he will uproot. Even R. Shimon forbids a Pesik Reishei.]

Alternative text (R. Tam): The correct text is that of R. Chananel, "and if not, like the Hechra of a small spice mortar". Hechra is the leg, like "Kar'ei ha'Mitah."

Support: The Yerushalmi explains like this "like the leg of a small spice mortar."

Explanation: This is an independent matter. I.e. one may clean with it even if it is bigger than an egg, or if there is more than a handful, one may take all of them. Since they have an Ed (mark from being used to clean oneself), all were prepared.

Explanation #1 (Rashi): [May one take them up to the roof, or] are we concerned for excess exertion?

Question (Ri): [Afterwards, Ravina] asks [from Chachamim,] who forbid taking a chip in front of him [to clean his teeth]. He should challenge our entire Sugya, which permits moving pointy rocks [to clean oneself]!

Explanation #2 (Ri): [Rabah bar Rav Shila] asks here because the privy is nearby on the roof, and he can prepare there before Shabbos;

[Rav Chisda] answered that even so, it is permitted. Therefore, [Ravina] asked that one may not take a chip from in front of himself, because he could have prepared before Shabbos;

However, he could not challenge our entire Sugya, for it was normal to defecate in the field, and the privy was far away. Chachamim did not obligate him to enter [rocks] there from before Shabbos. And even if he will prepare, perhaps someone else will take them!

Assertion (Ri): "From the feeding trough" is not precise. Rather, it is what is proper for the feeding trough,

Suggestion: Perhaps when it is not in the feeding trough it is forbidden, for it is Batel to the ground!

Rejection: A Mishnah in Beitzah (33a) says that Chachamim say "he may take a chip from in front of him and light [with it on Yom Tov]." This shows that it is not Batel [to the ground]!

Implied question: Why do [Chachamim] not permit [a chip] to clean his teeth, rather, [only] to light?

Answer: They hold that wood is only for burning. (Therefore, any other use requires designation from before Shabbos.) However, something proper for an animal's trough is permitted even to clean his teeth.

R. Eliezer, who holds there that one may take a chip from in front of him to clean his teeth, and he may gather from the Chatzer and light, he holds that what is in the house is prepared for anything he wants, even to clean his teeth. However, what is in the Chatzer is prepared only for burning.

Explanation (Rashi): Here, "liable" means lashes mid'Rabanan, since Reish Lakish permits. (He would not permit if there were a Chiyuv mid'Oraisa.)

Question (Ri): In Gitin (10b), R. Yochanan said that if a flowerpot with a hole was resting on pegs, R. Yehudah and Rabanan argue about it. R. Yehudah exempts from Ma'aser, like he distinguishes between a boat that scrapes [the ground under the water] and one that does not scrape. (What grows in the latter is exempt from Ma'aser.) Chachamim obligate [in both cases];

Rava said, perhaps this is not so. Rabanan [obligate] only regarding a boat, for there is no interruption of air (between the ground and what is growing), but a flowerpot [on pegs], in which air interrupts, even Rabanan [could] agree [that it is exempt]!

In our Sugya, we consider it to be attached mid'Oraisa even if he put it on pegs. He is liable for detaching only mid'Rabanan!

Answer (Ri): Our Sugya disagrees with Rava's rejection there.

Question: In Bava Kama (102a) and Avodah Zarah (7a) it says that in two Masechtos, Ein Seder l'Mishnah. (When Mishnayos in two Masechtos contradict each other, we do not know which was taught last, to say that Rebbi concluded like it);

Here (Davar she'Eino Miskaven), there is a Stam Mishnah in Nazir, and an argument in Beitzah (23b). R. Yehudah says that all Kelim may not be dragged on [an earth] floor [lest it make a furrow], except for a wagon, for it compresses [the earth, but does not make a furrow], so the Halachah does not [necessarily] follow the Stam. Perhaps it is Stam v'Achar Kach Machlokes (the argument was taught last)!

Suggestion: R. Yochanan holds that even regarding Stam v'Achar Kach Machlokes, the Halachah follows the Stam.

Rejection: We conclude in Yevamos (42b) according to R. Yochanan "the one who asked the question, do not be concerned for him. It is a Stam v'Achar Kach Machlokes, and the Halachah does not follow the Stam!"

Answer (R. Shmuel of Vardon): Regarding Machlokes v'Achar Kach Stam in one Maseches, all agree that the Halachah follows the Stam, like it says in Avodah Zarah (7a) regarding the ruling like R. Yehudah, that whoever retracts has the lower hand. The Gemara asks "this is obvious! It is Machlokes v'Achar Kach Stam!"

However, in two Masechtos, all [other] Amora'im hold that the Halachah does not follow the Stam, and R. Yochanan holds that even in two Masechtos, the Halachah follows the Stam;

Or, if there is a Stam Mishnah and an argument in a Beraisa, [R. Yochanan holds that] presumably the Stam was taught last. We should not say that first Rebbi taught Stam, and later he retracted from his ruling.

Remark: Amora'im argue according to R. Yochanan (whether or not he taught this general rule), like it says in Chulin (43a).