When it's not clear that a couple has either gotten married or (a different couple) divorced... where witnesses are essential. Plus, the case of Bar Shtaya and his property and testimony that can't be used as determinate. Also, a new mishnah, with another yibum case - this time, where 3 brothers are married to 3 women who are not related to each other. It's a case of ma'amar, 2 husbands (brothers) who die, and the question of 2 yibum bonds to two men (or is that even a thing).