1. May a witness testify that another witness told him that a firstborn animal received a blemish naturally?
2. If a person testifies that an animal not known to be a firstborn animal is indeed a firstborn, but it also naturally received a blemish, he is believed.
3. There is a dispute about whether even a Kohen who is a Chaver is suspected of causing a blemish to a firstborn animal.
4. The Gemara discusses the issue of whether any claim a person makes that can be verified is believed.
5. A person is believed to say that a blemish happened naturally to a doubtful animal of Ma'aser Behemah.
6. There is a discussion in the Mishnah about whether an expert is needed to rule on an obvious blemish.
A BIT MORE
1. Rav Asi: The Rabanan allowed such testimony only in the case of testifying that a woman's husband died, but not for any other matter. Rav Ashi: The Rabanan permitted such testimony in any case in which the testimony of a woman is acceptable (including the blemish of a firstborn animal).
2. This is based on the concept, "ha'Peh she'Asar Hu ha'Peh she'Hitir" -- "The mouth that forbade is the mouth that permits."
3. Rebbi Yehoshua: He is not suspected. Raban Gamliel: He is suspected.
4. The Gemara suggests this concept as a reason for the Mishnah's ruling that a Kohen is believed to say that he showed a blemish to a certain expert who agreed that it is a blemish.
5. This is because a person could make a blemish on every animal in his entire herd before he separates Ma'aser Behemah, ensuring that the animal that turns out to be Ma'aser Behemah cannot be offered as a Korban.
6. Tana Kama: Even three commoners may rule on an animal that was blinded or had a leg cut off. Rebbi Yosi: An expert is always required, even if the blemish seems obvious.