Herbenick invited me to sit in on the Human Sexuality class she was about to teach, one of the most popular courses on Indiana’s campus. She was, on that day, delivering a lecture on gender disparities in sexual satisfaction. More than one hundred fifty students were already seated in the classroom when we arrived, nearly all of them female, most dressed in sweats, their hair pulled into haphazard ponytails. They listened raptly as Herbenick explained the vastly different language young men and young women use when describing “good sex.” “Men are more likely to talk about pleasure, about orgasm,” Herbenick said. “Women talk more about absence of pain. Thirty percent of female college students say they experience pain during their sexual encounters as opposed to five percent of men.” The rates of pain among women, she added, shoot up to 70 percent when anal sex is included. Until recently, anal sex was a relatively rare practice among young adults. But as it’s become disproportionately common in porn—and the big payoff in R-rated fare such as Kingsman and The To Do List—it’s also on the rise in real life. In 1992 only 16 percent of women aged eighteen to twenty-four said they had tried anal sex. Today 20 percent of women eighteen to nineteen have, and by ages twenty to twenty-four it’s up to 40 percent. A 2014 study of heterosexuals sixteen to eighteen years old—and can we pause for a moment to consider just how young that is?—found that it was mainly boys who pushed for “fifth base,” approaching it less as a form of intimacy with a partner (who they assumed would both need to be and could be coerced into it) than a competition with other boys. Girls were expected to endure the act, which they consistently reported as painful. Both sexes blamed that discomfort on the girls themselves, for being “naïve or flawed,” unable to “relax.” Deborah Tolman has bluntly called anal “the new oral.” “Since all girls are now presumed to have oral sex in their repertoire,” she said, “anal sex is becoming the new ‘Will she do it or not?’ behavior, the new ‘Prove you love me.’” And still, she added, “girls’ sexual pleasure is not part of the equation.” According to Herbenick, the rise of anal sex places new pressures on young women to perform or else be labeled a prude. “It’s a metaphor, a symbol in one concrete behavior for the lack of education about sex, the normalization of female pain, and the way what had once been stigmatized has, over the course of a decade, become expected. If you don’t want to do it you’re suddenly not good enough, you’re frigid, you’re missing out, you’re not exploring your sexuality, you’re not adventurous.