The Sex Files

One night a few years ago, Mary Roach was in bed reading in Film Quarterly about the movies that sex-study pioneers Masters and Johnson made with their ''penis camera.'' ''Researchers built a machine equipped with lights and tiny cameras to film a woman's sexual response from the inside? I had no idea!'' recalls the Oakland-based writer. ''I was just like, 'Whoa, that's it! Next book!''' And so in Bonk, Roach tackles the funny science of sex with the same gusto she brought to the funny science of cadavers in the 2003 best-seller Stiff and the funny science of the afterlife in 2005's Spook. When Roach, 49, wasn't requesting odd-sounding titles from libraries, she was taking trips to London, Cairo, and Denmark, where she studied insemination at — eek — a pig farm. The hardest thing to watch, she says, was a penile implant in Taiwan. ''I'm the sort of person who, even though I'm a little ill at ease with it, I've got my face so close that they need to say, 'Ms. Roach, we need you to step back a bit.' Because it's all fascinating.''