With her bestselling Stiff, Mary Roach wrote an intelligent, understandable, and, most importantly, hilarious book about the art and science of death. In her newest book, Bonk, Roach discusses the art and science of fucking. She introduces the reader to a penis surgeon who talks like Yoda, a meeting of sex-machine aficionados, and the difficulties of scientifically observing the cervix during heavy intercourse. It can be said, without hyperbole, that she's the world's funniest science writer. (Town Hall, 1119 Eighth Ave, 652-4255. 7:30 pm, $5.)