how the hell

A man was talking to his friend at the bar. The friend said "Did you know that 9 out of 10 women with brown eyes cheat on their husbands?" "No, I didn't know that." The man replied. "So what color are your wife's eyes?" asked the friend. The man replied, "I'm too drunk to remember. Geez, I better go home and find out." So the man hurries home to find his wife in bed and asleep. The man carefully lifts his wife's eyelid and exclaims, "Oh my God! Brown!" Suddenly, another man pops out from under the covers and exclaims, "How the hell did you know I was here?"