The female menstrual cycle is a rite of passage into womanhood that for centuries has been shrouded in mystery and taboo. Pliny The Elder, for one, believed that menstrual blood could turn crop fields barren. Just last century, one scientist floated a theory that menstrual blood contained a poison that caused women to turn wine into vinegar. Let's not even start on the rumours that a burnt toad can ease a heavy flow.