More on two women who marry two men, and get switched before the nisuin part.... Which leads to a broader discussion of one trying to do a mitzvah who ends up doing a sin, and the machloket on that between R. Yehoshua and R. Eliezer. In this case, mixing up babies who need circumcision, one on Shabbat. What korbanot would need to be brought? Plus, a case of terumah for the child of a kohen from a union that is not permitted to a kohen. And another key case: chametz that is terumah on erev Pesach (yes). What's the sin-offering liability for one who is trying to do the right thing. Their dispute is maintained throughout. Also, some spicy Gemaras - when the married women have separated from their husbands, and they cannot do yibum or have halitzah or remarry until 3 months have passed, to make sure that she isn't pregnant from the first husband. Then the Gemara gets into the possibility of her getting pregnant, depending on how many times the couple has slept together. Plus, those women from the house of R. Yehudah HaNasi, who were known as "Tamar," because they broke their hymens to make pregnancy possible the first time (though this is not the science, of course). Plus, a woman who has been alone for 10 years and hasn't had sex throughout that time, which seems to be an indication that she will not bear children afterwards, even in the event that she marries later - if she had had intent to never marry again. But for those who want to marry again, this contraception, as it were, won't kick in (as per R. Hisda's daughter with Rava).