“Having sex on your period is absolutely safe,” reassures OB-GYN and talk-show regular Dr. Laura Berman. Like most sex experts in the past half-century, Berman is ready to demolish old menstrual taboos and usher in a modern period. And like many educators, physicians, and cultural critics who have written about menstruation, she frames her recommendations within a historical narrative: in the old days, religious proscriptions and folk traditions labeled menstruating women as