So far, what Keith learned from Arnold, was that every month, a curse would come and attack a deflowered witch, and it wasn't that hard to tell.
According to Arnold, it was the punishment for being unable to keep one's chastity, and could even result in death from the intensity of heat and pressure converging within.
Knowledge passed from generation to generation of witches and wizards, a certain date for the curse to occur, and only once in a blue moon would it occur to have it a few days before or later than the exact day. The rough estimation of the time in that day was rather believable and common compared to it.
Keith had yet to experience it, ever since he had to accept this kind of request.
Although, the main indication of the said curse was certain, regardless of its rare occurrence or phenomenon.