The laws relating to the severe ritual impurity caused by this condition appear in (15:1-15) and in tractate Zavim.
Rav Huna teaches that the initial discharge of a zav will make him tameh under all circumstances. The second discharge, however, is not significant if it came about because of an ones – that some outside event precipitated it. The Mishna in Zavim (2:2) teaches that there are seven bedikot – things that are checked for – to ascertain whether the discharge may have been caused by something other than the disease. They are:
Ma’ahal – If he overate or ate foods that are known to lead to discharge
Mishteh – If he drank too much
Masa – If he carried a very heavy burden
Kefitzah – If he jumped from one place to another
Holi – If he was ill
Mar’eh – If he saw a woman (even if he did not have sensual thoughts)
Hirhur – If he had sensual thoughts (even if he did not see the woman)
There is some discussion about the definition of the last two bedikot. According to Tosafot, mar’eh refers to seeing a couple engaged in sexual relations; according to the Rambam it is when a man sees a woman and fantasizes about her. Others suggest that it means that a person sees a frightening event that panics him, which does not relate to thoughts of sexuality at all.