During intercourse, a man places his penis in a woman's vagina and moves it in and out while the woman moves her hips. The vagina is warm and soft, and it places pressure on the man's penis. These sensations, combined with the in-and-out movements, stimulate the penis, which causes the man to have an orgasm. During orgasm, the man's penis spasms and experiences a series of rhythmic contractions during which he ejaculates (releases semen into the vagina). The semen can make the woman pregnant. Because intercourse is usually very enjoyable, men and women often want to have intercourse a lot more often than they want to have a baby. Birth control lets them have intercourse while greatly reducing the chances of the woman getting pregnant.