Why does the Torah use the double expression "Im Tarof Yitaref"?
Oznayim la'Torah: Because when wolves attack, 1 the shepherds tend to band together to beat them off, and the Pasuk speaks where, despite the efforts of the shepherds, the wolves succeeded in snatching a sheep. 2
What is the significance of the 'Hey' in "ha'Tereifah Lo Yeshalem"?
Rashi: It indicates that he is only Patur for certain cases of Tereifah - via a wolf, a lion a bear or a snake, which he could not have prevented on his own, but not via a cat, a fox or a marten, which he could.
What exactly does "Yevi'ehu Eid" mean?
Rashi: He must bring witnesses to testify that it became a T'reifah be'Oneis. 1
Ramban (citing Ibn Ezra), Rashbam: He brings a part of the torn carcass 2 (Moshav Zekenim - or the skin) to substantiate his claim.
Bava Kama, 10b: The word reads "Ad" is punctuated with a 'Patach' and the last Pasuk reads "Yevi'eihu Ad ha'Tereifah, ha'Tereifah Lo Yeshalem (as if "T'reifah was written twice). And it teaches us that the owner of looking after the Neveilah lies on the owner, 6 not on the Mazik.
See also Torah Temimah (citing Aba Sha'ul in Bava Kama, 11a, who expounds on the word "Eid" - 'Yavi Adudah [the carcass] le'Beis-Din').
Seforno, citing Sotah 2a: Wherever the Torah says "Eid", it means two witnesses. See also Sifsei Chachamim.
Peirush Yonasan: Because the word "Eid", which can be read 'Ad', has a dual meaning. See also Na'ar Yonasan.
See Torah Temimah, note 142.
QUESTIONS ON RASHI
Rashi writes that he brings witnesses that it became Tereifah b'Ones. How will he have witnesses in the field?
Moshav Zekenim citing R. Asher: When the Shomer sees a lion coming, he calls to others.
Rashi writes that in some cases of Tereifah (Ones) he is liable, i.e. when he could have saved. If so, the one who holds that a renter is like a Shomer Sachar, what is the source to exempt him from Ones?
If he could have saved, this is not Ones! (I do not understand why Moshav Zekenim left this difficult. - PF).
Rashi writes that he brings witnesses that it became Tereifah b'Ones. What is the Chidush that witnesses exempt him?
Riva (14): In a place where witnesses are common, he must bring witnesses, and he is not believed through a Shevu'ah.