Bechoros Daf 18 בכורות דַף 18

In the Mishnah on the previous Daf, Rebbe Tarfon said that if two lambs appeared to be born simultaneously, הכהן בורר לו את היפה – the Kohen chooses for himself the better of the two lambs. The Gemara explains that he assumes ההוא דבריא נפק ברישא – the stronger one emerged first, pushing past its weaker twin. Rebbe Akiva says משמנין ביניהן – we rule that the “fat” is between them, i.e., the difference in value between the lambs. Rebbe Chiya bar Abba thought this means that the two parties divide the difference in value. However, Rebbe Yochanan proved that this cannot be, since Rebbe Akiva rules in the סיפא that המוציא מחבירו עליו הראיה – the burden of proof is on the one attempting to collect. Instead, Rebbe Yochanan says Rebbe Akiva holds the Kohen receives the כחושה – the weaker lamb. Accordingly, "משמנין" means שומן יהא ביניהן – the “fat” is the point of contention between them, and the owner tells the Kohen, אייתי ראיה דבכור הוא ושקיל – bring me proof that [the better lamb] is a bechor and take it.

The Mishnah taught, regarding the second lamb (which the owner keeps), וחייב במתנות – [the owner] is obligated to give the Kohanim’s gifts of זרוע לחיים וקיבה of this lamb. Rebbe Yose exempts the owner from מתנות. Rebbe Yochanan explains the reasoning of Rebbe Meir (the Tanna Kamma): הואיל וכהן בא עליו משני צדדין – because the Kohen challenges [the owner] from both sides and says, “If the animal is actually the bechor, it is entirely mine, and if not, הב לי מתנות מיניה – give me the מתנות from it!” Rebbe Yose holds עשו שאינו זוכה כזוכה – they treated [the Kohen] who did not acquire [the bechor] like one who already acquired it, and although it never came into his possession, כמאן דמטא לידיה – it is considered as if it came into his possession and he then sold it to a Yisroel in its blemished state in exchange for the (non-bechor) animal the Yisroel gave him. Thus, if the true bechor was given to the Yisroel, it was given as a sale, and is exempt from מתנות. [Accordingly, in the case of a single bechor, שאין חליפין ביד כהן – where there is no exchange in the Kohen’s hand,  Rebbe Yose would agree the owner must give the מתנות.]

The Mishnah taught that if one of the two lambs dies, Rebbe Tarfon says יחלוקו – they divide the remaining lamb’s value. Rebbe Ami said that Rebbe Tarfon must have retracted his original ruling, which assumes the stronger lamb is the bechor, and instead agrees that it is unknown which lamb was born first. Rebbe Akiva rules המוציא מחבירו עליו הראיה, and the owner keeps the remaining lamb. The Gemara ultimately explains their machlokes in a case where the Kohen is a shepherd in the owner’s חצר. Rebbe Tarfon holds the owner grants the Kohen the right to acquire bechoros with his chatzer, וניחא ליה דליתעביד מצוה [בממוניה] – for he is pleased that a mitzvah should be performed with his possessions. Since the חצר is jointly shared, this case is akin to two people who deposited animals with a shepherd and one animal died, שמניח רועה ביניהם ומסתלק – that the shepherd leaves the remaining animal between [the owners] and withdraws; they then divide it between themselves. Rebbe Akiva holds that the owner does not grant the Kohen rights in the חצר, since he stands to lose by doing so. Thus, the case is akin to one who left his animal with someone who has his own animals; if one dies, we rule המוציא מחבירו עליו הראיה.