"Group" sex: Pesachim 112a

When a divorced man marries a divorced woman, there are four opinions in the bed.

The danger of pairs: Pesachim 110b

I learned part of an extremely long section on superstitions regarding pairs. Things in twos (for example, having two beers rather than one or three) was considered dangerous. It made you vulnerable to both demons and witchcraft. That's right, the Rabbis of the Talmud believed in both.

I found the length and detail of this section a bit tedious (and, well, embarassing), but found it worthwhile when I came upon this statement. 'The general rule is, anyone who is strict [about the superstitions related to pairs], they [the demons and witches] will be strict with him. For anyone who is not strict, they [the demons and witches] with not be strict with him.' Essentially, these things have only the power you give them, or as a someone I know used to say, you live in the world you create.