The Gemara analyzes this ruling of the mishna: A half-kav of bones, yes, a nazirite must shave if he contracts impurity from them; a quarter-kav of bones, no, he does not. What are the circumstances? If we say that they contain bones that are a barley-grain-bulk, let the tanna of the mishna derive the halakha that it imparts ritual impurity due to the fact that it is a bone that is a barley-grain-bulk. Rather, the mishna is referring to a situation where it has been made like flour. In that case, a half-kav of bones render people and items impure in a tent, although they do not include a bone the volume of a barley-grain-bulk.

§ The mishna taught that a nazirite shaves for a limb severed from a corpse and for a limb severed from a living person, upon either of which there is a fitting quantity of flesh. The Gemara asks: If there is not a fitting quantity of flesh upon them, what is the halakha? Rabbi Yoḥanan said: The nazirite does not shave for them. Reish Lakish said: The nazirite does shave for them.

The Gemara explains their respective opinions. Rabbi Yoḥanan said: The nazirite does not shave for them, as the tanna teaches in the first clause of the mishna in the list of sources of ritual impurity for which a nazirite must shave: For a limb severed from a corpse and for a limb severed from a living person that contains a fitting quantity of flesh. One can infer from this: Those upon which there is an olive-bulk of flesh, yes, he must shave for them, but if there is not that amount of flesh upon them, no, a nazirite need not shave due to them.

And Rabbi Shimon ben Lakish says that he shaves, employing the following reasoning: From the fact that the mishna does not teach the following in the latter clause, i.e., the subsequent mishna (54a), in the list of sources of impurity for which a nazirite need not shave: A limb that does not contain a fitting quantity of flesh, one can infer that a nazirite is obligated to shave for a limb of that type.

And Rabbi Yoḥanan could have said to you, in response to Rabbi Shimon ben Lakish’s argument: The fact that the mishna omits this case from the list is not proof, as the tanna does not teach in the latter clause anything that can be understood by inference from the earlier mishna.

The Gemara raises a difficulty against this claim of Rabbi Yoḥanan: But the first clause of the mishna lists the case of a half-kav of bones, which indicates: A half-kav of bones, yes, a nazirite must shave for that; a quarter-kav of bones, no, he is not obligated to shave for that. And yet the tanna teaches in the latter clause that a nazirite does not shave for a quarter-kav of bones. This shows that the next mishna does not rely on the rulings of this mishna. Rather, it lists all the items for which a nazirite need not shave.

The Gemara rejects this argument: There, had the tanna not taught a quarter-kav of bones, I would say that he need not shave even for touching it or carrying it. For this reason it was necessary for the mishna to teach the case of a quarter-kav of bones, to indicate that it is only for their ritual impurity contracted in a tent that a nazirite does not shave.

The Gemara raises a further difficulty: But the mishna lists a half-log of blood among those sources of impurity for which a nazirite must shave, from which you can learn that for a half-log of blood, yes, he shaves; for a quarter-log of blood, no, he does not shave. And yet the latter clause of the mishna teaches that he need not shave for a quarter-log of blood. The Gemara answers: It is also necessary to state this halakha unambiguously there, to exclude the opinion of Rabbi Akiva, as Rabbi Akiva said: A quarter-log of blood that comes from two corpses renders people and items impure in a tent, whereas the mishna simply states: A quarter-log, which indicates that all of the blood comes from a single corpse.

The Gemara analyzes the dispute between Rabbi Yoḥanan and Reish Lakish: What are the circumstances of this limb severed from a corpse that is not covered by sufficient flesh? If it contains a bone that is a barley-grain-bulk, what is Rabbi Yoḥanan’s reason for maintaining that a nazirite does not have to shave for this ritual impurity? A bone of this size imparts impurity even if there is no flesh upon it. And if it does not contain a bone that is a barley-grain-bulk, what is Reish Lakish’s reason for saying that a nazirite must shave due to this bone? The Gemara explains that Reish Lakish could have said to you: Actually we are dealing with a limb that does not contain a bone that is a barley-grain-bulk, and even so the Merciful One includes it as a source of ritual impurity.

This is as it is taught in a baraita: “And whoever in the open field touches one who is slain by the sword, or one who dies on his own, or a bone of a man, or a grave, shall be unclean seven days” (Numbers 19:16). This verse is expounded by the Sages as follows: “In the open field”; this is referring to the halakha of one who overlies a corpse, even without touching it. “One who is slain”; this is referring to a limb slain, i.e., severed, from a living person, that contains enough flesh for the limb to heal.

The Sages further derive from the phrase “one who is slain by the sword” that the legal status of a metal sword in terms of its degree of ritual impurity is like that of one who is slain, i.e., a metal implement, e.g., a sword, that was rendered impure through contact with a corpse is impure to the same degree of severity as a corpse itself. “Or one who dies on his own”; this is a limb that was slain, i.e., severed, from a corpse and is covered with enough flesh that it would heal if he were alive. “Or a bone of a man”; this is a quarter-kav of bones. “Or a grave”; this is a sealed grave, which imparts impurity when there is less than a handbreadth between the corpse and its cover.