(Rava): I used to think that a Siman is better than Tevi'as Ayin (recognition), for we return a lost object (to anyone) based on a Siman, but only a Chacham receives through Tevi'as Ayin.
Retraction (Rava): The above teachings show that recognition is Adif. (Mesores ha'Shas points to Tosfos Berachos 50a DH Ela, who says that sometimes 'Adif' does not mean 'better', rather, 'as good.')
Support #1 - Question: How is a blind man (or any man, at night in the dark) permitted to cohabit with his wife? (Perhaps it is a different woman!)
Answer: Surely, we rely on Tevi'as Ayin (recognition) of her voice.
Likewise, we may rely on visual recognition!
Support #2 (R. Yitzchak brei d'Rav Mesharshiya): If two witnesses testify about a murder:
If they do not recognize the murderer but they know Simanim on his body and clothing, we do not kill him;
If they recognize him, we kill him.
Support #3 (Rav Ashi): If a man asks a messenger to summons Ploni, and he gives Simanim describing Ploni, he is unsure if the messenger will find him;
If the messenger recognizes Ploni, he will surely find him.
REMOVING THE GID
(Mishnah): When removing the Gid ha'Nasheh, one must remove all of it;
R. Yehudah says, he must remove (only) enough to fulfill the Mitzvah of removing it.
If one eats a k'Zayis of the Gid he gets 40 lashes;
If he ate a whole Gid, even if it is not a k'Zayis, he is lashed.
If he ate a k'Zayis of each Gid, he gets 80 lashes;
R. Yehudah says, he gets 40 lashes.
(Gemara): Bar Piyuli was removing the Gid for Shmuel. He was just cutting off the top.
Shmuel: You must cut deeper. Had I not seen, you would have fed me Isur!
Bar Piyuli dropped the knife. Shmuel consoled him. 'I am not angry. The one who instructed you holds like R. Yehudah.'
(Rav Sheshes): Bar Piyuli was removing what R. Yehudah requires to remove mid'Oraisa.
Objection: This implies that he did not remove what R. Yehudah forbids mid'Rabanan. Who would instruct him to do so?!
Correction (Rav Sheshes): Rather, Bar Piyuli was removing what must be removed mid'Oraisa. He left what R. Meir forbids mid'Rabanan;
R. Yehudah permits those remnants even mid'Rabanan.
(Mishnah): If one eats the Gid...
(Shmuel): The Torah forbids only the part of the Gid on the Kaf (the meat at the end of the thigh) - "Al Kaf ha'Yarech."
(Rav Papa): Tana'im argue about this;
(Beraisa): If one ate a whole Gid, even if it is not a k'Zayis, he is lashed;
R. Yehudah says, he is lashed only if it is a k'Zayis.
Chachamim are Mechayev for less than a k'Zayis, because it is a Briyah (a complete creation);
R. Yehudah says, the Torah forbids eating the Gid. (Less than a k'Zayis is not considered eating.)
Chachamim: No. It says "Lo Yochlu" to punish for a k'Zayis of a large Gid (but not to exempt eating an entire small Gid.)
R. Yehudah: "Asher Al Kaf ha'Yarech" teaches this! (One is liable for eating just the part on the Kaf.)
Chachamim: No, that teaches Shmuel's law. (Only the part on the Kaf is forbidden.)
R. Yehudah: It says "ha'Yarech" - the Gid is forbidden throughout the entire thigh.
Chachamim: No, that teaches that the (inner) Gid which stretches throughout the entire thigh is forbidden.
Question: "Kaf" is needed to permit the Gid of a bird! (It has no Kaf.)
Answer: It says "Kaf" twice in the Parshah.
A GID THAT WAS COOKED WITH MEAT
(Mishnah): If a thigh was cooked with the Gid ha'Nasheh inside:
If it is Nosen Ta'am (imparts taste) to the thigh, the thigh is forbidden.
If meat and turnips (of volumes like those of the Gid and thigh, respectively) were cooked together and the meat would give Ta'am to the turnips, we (are stringent, and) assume that the Gid gives Ta'am to the thigh.
If the Gid ha'Nasheh was cooked with permitted Gidim -
If we recognize the Gid ha'Nasheh, we remove it, and the others are permitted if the Gid ha'Nasheh was not Nosen Ta'am (to them);
If we cannot recognize the Gid ha'Nasheh, they are all forbidden.
The liquid in the pot is forbidden if the Gid ha'Nasheh was Nosen Ta'am.
The same applies to a piece of Nevelah or a Tamei fish cooked with other pieces -
If we recognize the forbidden piece, we remove it, and the rest are permitted if the Isur was too small to give Ta'am;
If we cannot recognize the Isur, all the pieces are forbidden.
(Gemara - Shmuel): This is only if the thigh was cooked (with water). If it was roasted, it is permitted (but one may not eat the meat around the Gid).
Question: Rav Huna taught that if a kid that was roasted with its Chelev, even the ear is forbidden (because the Chelev gives Ta'am to the entire kid)!
Answer: Chelev is different. It bubbles up and spreads.