Exode 22:12

If it hath been torn by a wild beast, let him bring witnesses, or bring him to the carcase: because for that which is (so) torn he shall not make restitution.

IF IT BE TORN IN PIECES — “by a wild beast. ‘Y’VIEIHU EID’ — let him bring witnesses that it has been torn in pieces by accident, and then he will be free from paying.” This is the language of Rashi.
But one may wonder. Why did Scripture mention specifically here [in the case of the animal being torn to pieces by a wild beast], the necessity of having witnesses, since in this [very same section of the law of the paid guardian] it has already said above, [in the cases where the animal dies, or is hurt, or captured], The oath of the Eternal shall be between them both [i.e., between the owner of the animal and the guardian], and the law in all cases is alike: if there are witnesses that the animal died, or was hurt, or captured, he is free from paying and so also if it was torn in pieces by a wild beast, and if there are no witnesses he must take an oath in all cases, and if he does so, he does not pay? Perhaps Scripture speaks of the customary manner, for when an animal dies in his master’s crib or it goes up to the top of a crag and is hurt, there is usually no man seeing it; so also if it was captured by armed bandits who came upon it and took it from the flock and went away [there are usually no witnesses]. But when a lion or bear attacks, a multitude of shepherds is called forth against it,, 31:4. and therefore Scripture says that he should bring the shepherds to court, and [upon their testimony] he will be freed from the liability of payment.
Or we may explain that Scripture intends to establish the law enunciated by Isi ben Yehudah, who says, “No-one seeing it — he is free [from payment but he must swear]; but if there are witnesses who could testify in this matter, let him bring the witnesses and only then will he be free.” And the explanation thereof is as follows: If the accident happened [to the animal entrusted to his guardianship] in a place where people are present the whole day, we do not rely upon his oath but instead he must bring witnesses, and where an animal is torn in pieces by a wild beast, it is generally the case [that other people are present besides the guardian], and therefore Scripture required him to bring witnesses.
Rabbi Abraham ibn Ezra explained: y’vieihu eid — “let him bring part of the torn animal as witness, two legs, or a piece of an ear in proof of his statement.” And I have seen it explained thus in the Mechilta of Rabbi Shimon ben Yochai: “Aba Shaul said, he should bring the carcass, as it is said, Thus saith the Eternal, as the shepherd rescueth out of the mouth of the lion, two legs etc.”

יביאהו עד, any part of the carcass of the animal which had been devoured by a predator is acceptable as evidence of what had happened to it. We have a verse in Amos 3,12 describing the situation, כאשר יציל הרועה מפי הארי שתי כרעים או בדל רוזן, “as a shepherd rescues from a lion’s jaws two shank bones or the tip of an ear.”

יביאהו עד, we already explained that whenever the Torah uses the word עד in the singular mode what is meant are two witnesses who are acceptable to the court. אם טרוף יטרף, by some wild beast; presumably someone did witness the occurrence seeing there must have been other shepherds in the vicinity. What kind of testimony is expected of these witnesses?

הטרפה, that the situation in which the animal had been mauled or eaten was the kind of accident which the shepherd guarding it could not have been prevented by exercising greater care.

לא ישלם, the shepherd does not have to make restitution. If, however, the predators had eaten the animal under discussion due to insufficient supervision on the part of the shepherd, the shepherd has to make restitution. (compare Baba Metzia 93) In determining a reasonable fight which the shepherd has to put up against predators, Rashi quoting the Mechilta says that a solitary wolf is not something against which the shepherd is defenseless, neither are two dogs. Naturally, smaller animals and rodents are not considered as posing a threat to man.