Bechoros Chapter 4, Mishnah 3. We now move on to the topic of the mumcheh - the professional expert. To determine if a bechor has a permanent blemish, a lasting blemish and a defect that will not pass, as opposed to a passing blemish which is only temporary, it must be shown to a mumcheh.
Who is the mumcheh:
It is not enough for a person to be well-versed in the laws of blemishes, nor is it enough for him to be an expert in the relevant veterinary knowledge, nor even for him to be a rabbi. All of these are indeed required, but they are not enough. Official semichah and permission are required from a beis din in the Land of Israel, from the Sanhedrin, or from the Nasi himself, and without it a person is not permitted to rule and permit bechoros. This is the third category of semichah:
"Yoreh yoreh" - permission to rule on matters of permissible and forbidden.
"Yadin yadin" - permission to serve as a judge in a beis din for monetary matters.
"Yatir yatir" - permission to permit bechoros, which is given exclusively by a beis din in the Land of Israel, the Sanhedrin, or the Nasi himself.
Slaughtering the bechor and then showing its blemish:
What is the law regarding someone who did not consult a mumcheh prior to slaughter, but slaughtered his animal out of certainty that it had a blemish, and only afterward showed the blemish to the qualified and appropriate person? This is the case that our Mishnah deals with: "Hashochet es habechor umareh es mumo" - one who slaughters the bechor and then shows its blemish. He acted in reverse order, as he should have shown the blemish first and received permission to slaughter, and only then slaughtered.
The view of Rabbi Yehuda: If after the fact, the mumcheh examined the blemish and determined that it will not heal and is a permanent blemish - even though he acted improperly by not consulting the mumcheh in advance, since the mumcheh confirms the matter, he is permitted to eat the animal.
The view of Rabbi Meir: "Ho'il venishchat shelo al pi mumcheh - asur" - since it was slaughtered without the instruction of a mumcheh, it is forbidden. The person did not act according to proper procedure, since it is obligatory to first show the bechor to a mumcheh and slaughter it based solely on his ruling, and not beforehand. Therefore, he is penalized and may never eat the animal. It is worth noting that it is possible we are dealing here with a Torah scholar, and nevertheless, he is penalized.
The reasons for the dispute:
Rabbi Meir's view is based on the concern that even when it seemingly appears clear that the animal had a blemish, a change may have occurred in it after death, especially when the blemish is in the eye: the eye changes and becomes distorted due to the manner of death, and consequently the mumcheh can no longer state with certainty whether a permanent blemish is before him or not. Therefore, after the fact it is too late, and we do not eat it.
Rabbi Yehuda replies that this is indeed true, but there are many blemishes that are not in the eye and are not affected at all by the death. For example, when an animal is missing a leg - it is absolutely clear that it has a blemish, and therefore it should be permitted.
Rabbi Meir and Rabbi Yehuda agree regarding those blemishes that are liable to change due to death, such as a blemish in the eye. However, Rabbi Meir maintains that once we permit people to slaughter first and ask later, they will take matters into their own hands and many mishaps and errors will result from this. Therefore, he established a sweeping rule: one must show the bechor to a mumcheh first, and if he did not do so - it is forbidden for him to eat this bechor.
Practical Halachah Nowadays:
Nowadays, we do not have an ordained expert who has the authority to permit a firstborn animal (bechor). The Shulchan Aruch rules that a Jew who has a bechor in his possession and cannot show it to an expert may show it to three men - not actual ordained experts, but three people who are knowledgeable in the field. Three rabbis are called, and if they are jointly convinced that there is a permanent blemish before them, they have the authority to permit the bechor. This is indeed what is done in practice nowadays.
In summary: In this Mishnah, we learned that the determination of a permanent blemish in a bechor is entrusted to an expert who received "Yatir, yatir" ordination from a court in the Land of Israel, from the Sanhedrin, or from the Nasi. The Tanna'im disagree regarding one who slaughters the bechor and only afterward shows its blemish: Rabbi Yehudah permits it after the fact if the expert confirms that the blemish is permanent, and Rabbi Meir forbids it and imposes a penalty, due to the concern that the animal's condition changed after death and the concern of subverting the proper procedure. In practice nowadays, in the absence of an ordained expert, we permit the bechor based on three people who are knowledgeable in the field.