Remember when you first discovered sex? In your 6-year-old mind, your parents had done the dirty twice—once to conceive you, and a second time to crank out your little sister. Then, around the 6th grade, you realized that propagation is only a small part of sex. In fact, it’s just one of 237 reasons humans hook up, according to a recent University of Texas study. Although you don’t need a white coat to explain why you love sex, her motivations for sealing the deal often seem rather . . . mysterious. Fortunately for you, the researchers surveyed hundreds of women to pull back the sheet on sex. Here are the top 15 reasons she sleeps with you, and how to, ahem, encourage her along.
You’re a Good Kisser
Your move: So what if you’re not a hormonal 16-year-old. You’re never too old for a steamy makeout session—in fact, a well-executed kiss could be your golden ticket to the main event. According to a recent study in the journal Evolutionary Psychology, women are far less likely than men to have sex with a bad kisser. Sounds easy enough, right? Not so fast, cowboy—her definition of a stellar smooch may differ from yours. The researchers found that guys preferred wetter kisses with more tongue action than females did. Here’s what turns her crank: A partner who makes the first move, smells fresh, and caresses her while kissing. Oh, and pop in a breath mint. Women rated the taste of someone’s mouth as more important when deciding to continue kissing than men did.
It Seems Like the Natural Next Step in the Relationship
Your move: You’ve wined her, dined her, and wooed her, but still, no sex. The missing link? Commitment—it’s key to sexual motivation in women of all ages, according to a recent study in the Journal of Sexual Medicine. Don’t panic: It doesn’t necessarily require a ring. Research has repeatedly shown that making personal disclosures signals investment in a relationship. In other words, sharing intimate details shows you’re emotionally in it for the long haul, encouraging her to move forward physically.
You Caress Her
Your move: Stroke her forearm first. This area of the arm is packed with pleasure nerves that respond best to a touch traveling 1 to 10 centimeters per second, scientists report in the journal Nature Neuroscience. These “C-tactile” nerve fibers (also found on the legs and face) send signals to the limbic system, an area of the brain associated with trust and affection, says study author Hakan Olausson, M.D.
You Make Her Feel Sexy
Your move: Establish your compliments safety zone. “Listen to the things she says about herself. Watch the way she reacts when you touch certain areas,” says Chris Fariello, Ph.D, of the Council for Relationships. This clues you in to the body parts she’s insecure about—and lets you know where to tread lightly. “You may give a compliment, but she can turn it around and hear a negative,” he says. “If she’s self-conscious about her butt, and you say, ‘You have a great, round butt,’ she hears fat, not great.” When it comes to her sensitive spots, stick to universal compliments like, “Your butt looks great in those jeans.”
She’s in a Romantic Setting
Your move: You know the old cliché: Whisk her away to an exotic location, and you’re sure to score. That’s probably true, but not for the reasons you may think. It’s less the destination, and more the shared intimacy of “otherness”—or of being outsiders—that sets the mood, according to a 2005 study in the journal Tourism Management. Book a trip for two to a foreign country, and prearrange a tour guided by a local, which creates a greater sense of intimacy and disclosure, the scientists say.
Your Physical Appearance Turns Her On
Your move: Meatheads may rule your gym, but in reality, women prefer muscle definition over muscle mass, according to a recent UCLA study. When 141 women evaluated photos of shirtless men, they ranked lean, athletic-looking bodies as more desirable than both bulky and skinny types. Study author David Frederick, Ph.D., says that women perceive men with big muscles as threatening and also know that it takes time to build all that brawn—time you might not spend with them. “They’re looking for signs of not only health and fitness but also a potential commitment,” he says. To sculpt a lean, chiseled body, follow these 5 easy steps to burn fat and reveal muscle.
She Wants to Feel Emotionally Close or Connected
Your move: Start foreplay outside the bedroom—by raving about the free donuts at the office this morning. Sharing upbeat details about your day strengthens a relationship, say researchers at the University of Utah. Talking and listening “helps maintain emotional intimacy,” explains study co-author Angela Hicks, Ph.D. The study also found that venting about stressful incidents didn’t dampen a partner’s mood.
She Wants to Please You
Your move: If you’re striving for the Big O, start with the Big C: communication. “She may not have the sexual confidence to take charge,” says Linda Banner, Ph.D., author of Advanced Sexual Techniques. “You need to let her know what turns you on.” In a recent Boston College study, people indicated that talking about sexual behavior—sharing fantasies, turn-ons, and sexual dislikes, for example—resulted in both better sex and greater desire. Candidly chatting about sex helps her feel close to you, while also boosting her confidence in pleasuring you, the scientists say. The key: Initiate the talk outside the bedroom—79 percent of “unsatisfying” sexual conversations occurred between the sheets, the study reports.
She’s Caught Up in the Heat of the Moment
Your move: Even if she rolls over, it’s not too late to heat things up. Sidle up and spoon her (without poking anything into her back)—cuddling causes her testosterone to surge, a recent Canadian study found. Increased T levels may cause androgen receptors in her clitoris to switch on, leading to arousal, the scientists say. Bonus: Women feel more sexually attractive the morning after cuddling, the study found. Steamy shower sex, anyone?
She Realizes She’s in Love with You
Your move: A big business deal going down in Tokyo? Don’t hesitate to raise your hand for the job. Turns out, the old adage is true: Absence makes the heart grow fonder. A recent American Psychological Association study found that during travel-related separation, homebound partners’ positive feelings—closeness, meaningfulness, and mutual appreciation—declined, but then surged to an all-time high upon reunion. Just make sure to call while you’re away: Greater telephone contact during separation was key to minimizing negative feelings once the traveling partner returned.
She Thinks It’s Fun
Your move: First, show her how fun you can be outside the bedroom. A recent study in The Journal of Psychology found that women were 25 percent more likely to consider a man attractive if he had a good sense of humor, and were 31 percent more likely to consider him a suitable mate. Try exchanging naughty jokes via email while you’re apart—this adds an element of fun to your all-day foreplay.
She Needs Release or Feels Horny
Your move: Propose a horror movie marathon. “Being scared is physiologically arousing, and in the right company, it may eventually carry over to sexual arousal,” says Joanne Cantor, Ph.D., a professor emerita of communications at the University of Wisconsin, who studies the ways people are affected by media. After the movie, she may find your glances more erotically charged and your touches more stimulating, she says. If your date isn’t into over-the-top terror, à la Saw VI, watch classic thrillers instead, like The Silence of the Lambs.
She Wants to Express Her Love or Affection
Your move: Forget the elliptical, and ask her to hit the weights with you. A new University of Connecticut study found that resistance training increases free testosterone levels in women—a spike that also occurs when she’s head over heels. In a study  published in the Journal of Psychoneuroendocrinology found that hormonal changes occur in both men and women when falling in love. Women’s testorsterone levels rise, while men’s fall, the study found. After your workout, reinforce her rising T with a sweaty makeout session: “Male saliva has 10 to 15 times more testosterone than the female’s does,” says Louann Brizendine, M.D., author of The Female Brain. “So prolonged French kissing may give a woman enough of a boost in testosterone to stimulate her interest chemically.”
She Wants to Experience Pleasure
Your move: Give her a massage to trigger blood flow down below—in her feet, that is. Women need to warm up their feet and feel comfortable before they’re in the mood for sex according to a Eurpoean study. So try some reflexology, like this move from Bill Flocco, president of the American Academy of Reflexology: Support one of her feet in one hand while you use the fingers of the other hand to squeeze it gently and steadily. After a minute or so, place your thumb on the center of her sole and bend the thumb’s knuckle back and forth across the foot without ever losing contact with her skin. This will send “stimulating signals” to her entire body.
She’s Attracted to You
Your move: If you hope to take her home, you better play nice—tough guys don’t wow women, a recent study in the Journal of Experimental Social Psychology found. When researchers presented women with scenarios of men being harassed or insulted by other men, they preferred the guys that detached themselves from trouble. If you’re looking for her to notice you, keep tabs on your smiles. A 2011 British Columbia study found that women were least attracted to smiling, happy men, preferring those who looked proud and powerful or moody and ashamed.