As a segue from the Gemara’s discussion about squeezing on Shabbat the discussion turns to hearsay testimony. It is clear that in limited cases (e.g., when a woman’s ability to get married depends on it) such testimony is accepted. Can it be accepted to determine the status of a blemished firstborn animal?
The Torah commands one to give the firstborn offspring of kosher animals to a priest. During the Temple period, unblemished firstborn animals were offered as sacrifices, and their meat would be eaten by the priests. Blemished firstborn animals also belonged to the priests, and the priests could eat them as non-sacred meat once experts determined that the blemish is permanent.
Priests were suspected of purposely causing blemishes to firstborn animals so that they would be allowed to eat them. Consequently, the Sages decreed that priests could not eat the meat of a firstborn animal without testimony to the cause of the blemish. Since this testimony was required only to alleviate suspicion, the Sages were lenient with regard to its requirements.
We learn in the Gemara:
A dilemma was raised before the Sages about a related matter: With regard to hearsay testimony in testimony permitting a priest to eat a firstborn animal, what is the halakha?
After the destruction of the Temple, the Sages decreed that if a priest has the firstborn offspring of a kosher animal and it becomes blemished, he must bring witnesses to testify that he did not cause the blemish. As noted, priests were suspected of violating the prohibition against inflicting a wound on firstborn animals to enable them to eat the animals. The question here pertains to a case in which there is no one available who can testify that he saw firsthand how the animal was blemished, but there is someone who heard from an eyewitness how the blemish was caused.