Psst! There is a hip, hilarious and truly eye-opening cultural history of menstruation revealed in Flow. Elissa Stein’s latest book, with Susan Kim, Flow spans its fascinating, occasionally wacky and sometimes downright scary story: from mikvahs (ritual cleansing baths) to menopause, hysteria to hysterectomies—not to mention the Pill, cramps, the history of underwear, and the movie about puberty they showed you in 5th grade.