Semen is best known for what Woody Allen portrayed in his film, Everything You've Ever Wanted to Know About Sex... which is, of course, sperm. Happy little spermatozoa swim their way into the fallopian tubes where fertilization takes place. But sperm comprise only about 3 percent of semen. The rest is labeled seminal fluid: mostly water, plus about 50 compounds: sugar (to nourish sperm), immunosuppressants (to keep women's immune systems from destroying sperm), and oddly, two female sex hormones, and many mood-elevating compounds: endorphins, estrone, prolactin, oxytocin, thyrotrpin-releasing hormone, and serotonin. Until recently, scientists believed that the sole purpose of seminal fluid was to nourish and protect sperm on their way to fertilization. But now it appears that semen can actually spur ovulation, and what's more... help women feel happier.