Ice Bath
(Info)
The object of the ice bath is to put the person in a trancelike state. Werewolves will half-transform, and the trance will allow access to the subconscious. The induced hypothermia slows the person's heartrate down to almost none.
It is not a particularly safe procedure.
For some reason, the person is also held under the water during the bath, even though this is not necessary to induce hypothermia.