A woman walks into a store with her two children, a boy and a girl. The guy behind the counter looks at her, looks at her kids and asks, "Are they twins?" Confused, the woman replies, "No they're not twins. One's a boy and one's a girl. One's 7 and the other's 9. What could possibly make you think they were twins?" The clerk shrugs and replies, "I just couldn't imagine you getting laid twice."