1. If one inflicted a מום without knowing it permits the bechor (a gentile or child)

The next Mishnah relates an incident with an old ram whose hair was dangling because it was never shorn. A Roman official inquired about it and was told it was a bechor, ואינו נשחט אלא א"כ היה בו מום – and it may not be shechted unless it develops a blemish. The Roman took a spear and nicked its ear, and the Chochomim permitted it, since he did not know that intentionally blemishing the bechor permits it (מדאורייתא). He began to do the same to other bechoros, and the Chochomim prohibited them (since he now understood that a מום permits it). Similarly, children once tied several lambs’ tails together, and a bechor’s tail was torn off. The Chochomim permitted it, until they began to do so to other bechoros.

Rav Ketina says a מום inflicted by an idolator is only permitted if he said the bechor is forbidden אא"כ היה בו מום – unless it has a מום, but if he said "אם נעשה בו מום" – unless a מום is made in it, כמאן דא"ל זיל עביד ביה מומא דמי – it is as if he told him, “Go make a blemish in it,” and it is forbidden. Rava permits even this case.

1. One who kicked a bechor which was chasing him

The next Mishnah states: היה בכור ר[ו]דפו – if a bechor was chasing [someone], בעטו ועשה בו מום – and he kicked it and thereby inflicted a blemish in it, it may be shechted based on the מום. Rav Pappa says this only applies if he kicked it בשעת רדיפה – during its pursuit, but if he kicked it לאחר רדיפה – after its pursuit, it is forbidden. Although it seems obvious that he intends to blemish it (since he is no longer in danger), one might think צעריה הוא דמדכר – he is remembering his suffering and kicking the animal in anger, and it should be permitted. Therefore, Rav Pappa informs us otherwise. In another version, Rav Pappa says that the bechor is permitted even if he kicked it after it was no longer chasing him, because he is remembering the suffering he endured from this animal.

1. Who is believed to testify that a מום was not inflicted intentionally?

In the next Mishnah, the Tanna Kamma says, regarding מומין which can be man-inflicted, רועי ישראל נאמנין – “shepherds of Yisroelim” are believed to testify that they occurred naturally, but רועים כהנים אינן נאמנין – “shepherds of Kohanim” are not believed. Rabban Shimon ben Gamliel says he is believed about של חבירו – his friend’s bechor, but not about his own. Rebbe Meir says החשוד על הדבר לא דנו ולא מעידו – one who is suspected about something may neither judge nor testify about it. Amoraim debate if "רועי ישראל" refers to Yisroel shepherds working for Kohanim, or Kohanim shepherds working for Yisroelim. This depends on whether we are concerned a Yisroel shepherd would testify falsely for "לגימא" – merely to partake of the bechor’s meat with his employer, and whether a Kohen shepherd would testify falsely for his Yisroel employer (hoping to receive the bechor), and, regarding a Kohen shepherd for another Kohen, whether we are concerned for גומלין – their reciprocating favors for each other (i.e., that the employer will testify for the shepherd if he later has a bechor). Tannaim debate if two witnesses from “the market” (i.e., not from his household) are required, or if one’s own son or daughter may testify, or one outside witness suffices.