Keritot, Chapter Five, Mishnah Four
This mishnah continues to deal with the issue of doubtful sacrilege.
1) [If there was] a piece of hullin meat and a piece of sacred meat, and a person ate one of them and does not know which of them he ate, he is exempt.
a) Rabbi Akiba declares him liable for an asham talui.
2) If he then ate the second [piece], he is liable to a certain asham.
3) If he ate one [piece] and another came and ate the other, each of them is liable to an asham talui, the words of Rabbi Akiba.
a) Rabbi Shimon says: they together bring one asham.
b) Rabbi Yose said: Two people cannot bring one asham.
Section one: This is the same debate we saw in mishnah two of this chapter. According to Rabbi Akiva one must bring an asham talui for a doubtful case of sacrilege.
Section two: If he eats both pieces of meat, then we know for sure that he ate sacrificial meat, and he is obviously liable for sacrilege.
Section three: In this case, one person definitely ate a piece of sacrificial meat, but one person did not. According to Rabbi Akiva, they both bring an asham talui.
Rabbi Shimon agrees in principle with Rabbi Akiva, but says that in this case, there is no need for them both to bring the asham talui. They can together bring one asham, and make a stipulation, that if person A ate the sacrificial meat, it is his sacrifice, and if person B ate the sacrificial meat, it is his sacrifice.
Rabbi Yose says that such a system does not work and that two people cannot bring one asham. It seems that he would hold like Rabbi Akiva that each person must bring his own asham.