More than half the world's population menstruates. But for such a common biological process, how many of us really understand the mechanics of the menstrual cycle? Dr. Lauren Verrilli, 4th-year UW Ob-Gyn resident and soon to be reproductive endocrinology and infertility fellow at the University of Utah, joined the Women's Healthcast to explain what's happening during periods and dispel some common menstrual myths.