We talk with Dr. Shai Secunda about the Babylonian rabbis’ science of blood, breaking taboos through sex education, and menstruation as a cure for rabies.

Today, taboos about menstruation keep thousands of girls from attending school. For Jewish sages in late antique Persia, such beliefs led to laws that required women to stay away from their husbands during their periods and to wash at prescribed times. (Whether these laws were followed is another question!) Blood could pollute, yet it could also purify. And practices around menstruation may have helped religious communities define their identity.