Sexy surprises he'll love: catching a man off guard makes him feel lucky ... and in love (it's biology, baby!). Wow him and watch your bond grow.

* You know those blissed-out couples who can't seem to get enough of one another? Well, they don't possess a magical passion potion--they keep their love buzz strong by spicing things up. "Any time you throw in a surprise--a last-minute trip, an unusual date location, an unexpected gift--it sends a signal from your brain's reward center that stimulates the rest of the brain, including the areas that register love and bonding," says Read Montague, PhD, director of the Human Neuroimaging Lab at Baylor College of Medicine.

Novelty also triggers the same physical sensations--like stomach butterflies and sweaty palms--he (and you) got when your relationship was brand-new. And not only do these shared adventures make you feel giddy about one another all over again, they also tighten your bond, says certified sex therapist Darcy Luadzers, PhD, author of the upcoming book The 10 Minute Sexual Solution. So how can you bring on the thrills? From food fights to surprise skinny-dipping dates, Cosmo readers--and some very satisfied guys--share their shockingly fun and sexy secrets.

* "My boyfriend records law-school lectures and transcribes them later to study. I once cued the tape to a pause in the lecture, hit the record button, and said 'I'm so hot for you,' into it. He took a nice, long study break with me later."--Jen, 25

* "One time in bed, my girlfriend whispered to me in French. She could have just been saying 'Take out the trash,' but hearing her speak in that accent was an incredible turn-on."--Chris, 28

* "My girl ran a bath for me ... then hopped in. I'd never had my scalp massaged, and when she shampooed me, I felt tingles all over my body. The cherry on top was when she pointed to the shaving mirror in the shower, and I saw that she'd given me a wet, soapy faux-hawk."--Morgan, 29

* "During dessert, I spontaneously flicked a blob of ice cream at my boyfriend. He laughed and retaliated, and soon it was an all-out food fight. Eventually, we were both on the floor laughing. It's still our most memorable at-home meal, and cleaning up each other afterward wasn't bad either."--Kim, 21

* "Text him two words next time you're leaving work: no panties."--Bruce, 30