Why does the Pasuk repeat the Din of Michyah?
Rashi: To include a case where a Nega appeared on one of the twenty-four tips of limbs 1 which are initially precluded from Tum'ah because the Nega cannot be seen in one go, where the area became fatter and a Michyah appeared on it. 2
The tips of ten fingers and the toes, the tip of the nose, the tips of the ears, the tip of the Eiver ha'Milah and the nipples of a woman's breasts.
Refer to 13:14:151:1-3. and see Sifsei Chachamim.
Why does the Torah insert the word "u've'Yom"?
Rashi: To teach us that there are some days on which the Kohen does examine a Nega, and some days on which he does not - including a Chasan during the period of his Sheva B'rachos (both as regards the Chasan himself and as regards his clothes and his house) and all the days of Yom-Tov.
What is the word "Hera'os Bo ... Yitma" coming to preclude from the Din of Tum'ah?
Sifra: It precludes the head, the beard, a boil, a burn and a wound that was inflicted in other ways - all of which are not subject to Nega'im.
What is the Shi'ur of Basar Chai that renders the Metzora Tamei in this case?
Sifra: We learn from a Gezeirah Shavah "Basar Chai" "Basar Chai" from Pasuk 10 that the Shi'ur is a ke'Adashah (the size of a lentil).
QUESTIONS ON RASHI
Rashi writes that the Pasuk teaches about a Nega on one of the twenty-four extremal limbs that are normally excluded from Nega'im, and it became fatter. What forced him to say that, seeing as simply, the Pasuk is discussing someone whose body is covered with Tzara'as, and a part became healthy (Indeed, the Sifra explains that if a Nega is in a location which is excluded from Tzara'as, even if it became fatter, it is Tahor)?
Korban Aharon: Rashi did not learn from the Sifra but from the Tosefta, 2:12, which states that the tenty-four extremal limbs are excluded from Nega'im, but that, if they have a flat area the size of a Gris, they ar subjet to Nega'im. 1
Panim Yafos: Also Rashi discusses when the body was covered with Tzara'as, and a part became healthy. One might have thought that this is more stringent, and a Michyah of any size is Metamei, if the place widened and now it is eligible for a Nega and the Pasuk teaches us that the same Shi'ur (of ke'Adashah) applies.
Moshav Zekenim and Da'as Zekenim: The Pasuk is repeated to teach us that even though initially a location is subjet to Nega'im only if it has a flat area the size of a Gris, if the body is covered with Tzara'as, a Michyah ke'Adashah - such as a flat area - will suffice to reender him Tamei.
Panim Yafos: The Tosefta can be discussing where from the beginning they had a flat area the ssize of a G'ris. This is no proof however, that if a Nega is on a curved area, and afterwards it widened, it is Tamei!
Rashi writes that "u've'Yom" teaches us that there are some days on which the Kohen does examine a Nega. But the Gemara in Sanhedrin, 34b states that he does not examine a Nega at night, which the Gemara in Mo'ed Katan, 8a learns from the "Nir'ah Li" - 'Li ve'Lo Ori' (to me and not through my lamp!'?
