2,268. Teaching the Secrets of the Arayos

Hilchos Issurei Biah 22:16

A Torah scholar is not permitted to live in the same courtyard as a widow even if he doesn’t enter into seclusion with her unless his wife is with him; this is out of concern that suspicions might arise. Similarly, a widow may not raise a dog because suspicions might arise. A woman may likewise not purchase male servants, even if they’re minors, in order to prevent suspicions from arising.

Hilchos Issurei Biah 22:17

We don’t teach the secrets regarding prohibited relations to three students out of concern that while one student is asking questions, the other two will be discussing things between themselves and not listen. Since a person is aroused by sexual things, if a doubt arises regarding something he heard, he might end up permitting something prohibited. Therefore, these matters are only taught to two students so the one listening will pay full attention and remember what he hears from his teacher.