How could that possibility enter one’s mind? If that is so, the completion of that slaughter is a Temple service performed by another on Yom Kippur. And it is taught in a baraita: The entire Yom Kippur Temple service is valid only if performed by the High Priest.

The Gemara answers that this is what Rabbi Shimon ben Lakish is saying: One might have thought that if the slaughter was not completed by the other priest it would be not valid by rabbinic law, as it might enter your mind to say that there is an invalidation by rabbinic law. Therefore, we learned in the mishna: The majority of one siman in a bird or the majority of two simanim in an animal. The Gemara asks: And since there is not even an invalidation by rabbinic law, why do I need the other priest to complete the cutting of the simanim? The Gemara answers: There is a mitzva to complete the slaughter ab initio to facilitate the free flow of the blood.

§ Rabbi Shimon ben Lakish says in the name of Levi the Elder: Halakhic slaughter is accomplished only at its conclusion. And Rabbi Yoḥanan says: Halakhic slaughter is accomplished from the beginning to the end of the act.

Rava said in establishing the parameters of the dispute between Rabbi Shimon ben Lakish and Rabbi Yoḥanan: Everyone concedes in a case where a gentile slaughtered, i.e., cut, one siman and a Jew slaughtered one siman, that the slaughter is not valid even if slaughter is accomplished only at its conclusion, as an action rendering the animal a tereifa was performed at the hand of a gentile. Since slaughter by a gentile is not valid, the gentile renders the animal a tereifa.

In the case of a bird burnt offering as well, where one siman was pinched by a priest below the red line marking half the height of the altar, in accordance with the procedure of the sin offering, and one siman was pinched above the red line, in accordance with the procedure of the burnt offering, the pinching is not valid, as the priest performed an action appropriate for a bird sin offering below the red line, disqualifying it from being sacrificed as a burnt offering.

Rabbi Shimon ben Lakish and Rabbi Yoḥanan disagree only in a case where an individual cut one siman outside the Temple courtyard and one siman inside the Temple courtyard. According to the one who says: Halakhic slaughter is accomplished from the beginning to the end of the act, i.e., Rabbi Yoḥanan, one who begins the slaughter outside the Temple courtyard is liable for slaughter of a sacrificial animal outside the courtyard. According to the one who says: Halakhic slaughter is accomplished only at its conclusion, i.e., Rabbi Shimon ben Lakish, one who does so is not liable, as the conclusion of the slaughter, which is the determining factor, is performed inside the Temple courtyard.

Rabba bar Shimi said to Rava: The Master did not say that this was the crux of the dispute between Rabbi Yoḥanan and Rabbi Shimon ben Lakish. And who is the Master? It is Rav Yosef, who says that in a case where one cut one siman outside the Temple courtyard and one siman inside the Temple courtyard, all agree that the slaughter is not valid and the priest is liable to receive punishment, because he performed an action appropriate for a bird sin offering outside the Temple courtyard.

They disagree only in a case where one slaughtered the minority of each of the simanim outside the Temple courtyard and completed the slaughter inside the Temple courtyard. According to the one who says: Halakhic slaughter is accomplished from the beginning to the end of the act, i.e., Rabbi Yoḥanan, one who begins the slaughter outside the Temple courtyard is liable for slaughter of a sacrificial animal outside the courtyard. According to the one who says: Halakhic slaughter is accomplished only at its conclusion, i.e., Rabbi Shimon ben Lakish, one who does so is not liable, as he concludes the slaughter in an appropriate place.

Rabbi Zeira raises an objection from a mishna (Para 4:4): Anyone who is engaged in any part of the rite of the red heifer continuously from beginning to end transmits ritual impurity to the garments that he is wearing. And they disqualify the red heifer for use in the rite if they perform any other labor while engaged in any part of the rite of the red heifer.

If a disqualification befell the heifer during its slaughter, with regard to all those engaged in the rite of the red heifer, whether they engaged in the rite before the heifer was disqualified or after the heifer was disqualified, the heifer does not render garments that they are wearing impure. Since its slaughter was not valid it is disqualified from being used as a red heifer and therefore does not impart impurity. If it became disqualified at the time of sprinkling the blood of the heifer toward the opening of the Temple, with regard to those who engaged in the rite of the red heifer before it was disqualified, the heifer renders the garments that they are wearing impure. By contrast, with regard to those who handled the animal after it was disqualified, the heifer does not render the garments that they are wearing impure.

Rabbi Zeira elaborates: And if you say that halakhic slaughter is accomplished from the beginning to the end of the act, let the mishna also distinguish between disqualification at the beginning and at the end of the slaughter: If it became disqualified during slaughter, with regard to one who engaged in any part of the rite before it became disqualified, the heifer renders garments that he is wearing impure, and with regard to one who engaged in any part of the rite after it became disqualified, the heifer does not render the garments that he is wearing impure.

Rava said: Are you saying that the discussion concerns a case where the slaughter was invalidated? There it is different, because the matter was revealed retroactively, i.e., it was revealed that it was not a valid slaughter at all. Since at no stage of the slaughter was it valid, the heifer does not render the garments impure at all.

Rava said: If any aspect of that mishna is difficult for me it is this that is difficult for me: According to the one who says: Halakhic slaughter is accomplished only at its conclusion, let the mishna distinguish between two individuals in the preparation of a fit red heifer, even when the heifer was not disqualified. Let the mishna teach a case where they slaughtered it with two men, as the heifer does not render the first man who slaughters impure, as the slaughter did not yet begin, and the heifer renders the latter man impure.

Rav Yosef said: Are you saying that the discussion concerns a case of two men slaughtering one offering? Raise difficulties except for that, as we learn in a baraita with regard to the verse: “And when you sacrifice a peace offering to the Lord, you shall sacrifice it [tizbaḥuhu] that you may be accepted” (Leviticus 19:5), that the term “tizbaḥuhu” can be divided into two terms: You shall sacrifice [tizbaḥ] and it [hu]. From the term “You shall sacrifice [tizbaḥ],” it is derived that there will not be two people slaughtering one offering. From the full term “You shall offer it [tizbaḥuhu],” it is derived that one person may not slaughter two offerings simultaneously.

And Rav Kahana said, to explain the derivation of the first halakha in the baraita: Although the term “tizbaḥuhu” is vocalized in the plural, leading to the conclusion that two people may slaughter an animal together, nevertheless, because the word is written without a vav, it emerges that the phrase “You shall sacrifice it [tizbaḥehu],” in the singular, is written, indicating that two individuals may not slaughter the offering.

Abaye said to Rav Yosef: Wasn’t it stated with regard to this halakha that Rabba bar bar Ḥana says that Rabbi Yoḥanan says: This is the statement of Rabbi Elazar, son of Rabbi Shimon,