Can a guy tell if a girl's a virgin?

Is there any way a guy can know whether or not a girl is a virgin when they have sex? Does she always bleed if it's the first time?

Many people believe that bleeding after intercourse is a sign of virginity because it proves that the hymen — a thin, fleshy membrane that partially covers the vaginal opening — "broke." But not all women bleed the first time they have sex. Not only can hymen tissue simply stretch during penetration, rather than tear and bleed, but it is also very common for the hymen to rip before a woman ever has sex. Physical exercise, like riding a bike or doing gymnastics, injury to the genital area, or inserting a tampon, finger, or sex toy into the vagina can all cause the hymen to split. Sometimes there will be discomfort and blood when the hymen tears, or there may be no blood or pain at all. In fact, you may not even know when your hymen breaks.

On the other hand, post-sex bleeding can occur for a variety of reasons besides a broken hymen, such as different types of infections, polyps of the cervix or abnormal cervical cells, and a tear in the vagina from vigorous sex without enough lubrication.

So, while a man might assume that a woman who bleeds after sex is a virgin, the only way for him to know for sure is if she tells him.