A little girl runs out to the backyard where her father is working, and asks him, "Daddy, what's Sex?"
"OK," he thinks, "this day was bound to come, and I'm not going to let my little princess learn about sex from the streets."
So, he sits her down, and tells her all about the birds and the bees. He tells her about conception, sexual intercourse, sperms and eggs. He tells her about puberty, menstruation, erections, and wet dreams.
Then she asks, "Daddy, what is 'A Couple'?"
And he carries on, "A couple are the two people involved in sex, but this can also be two males or two females which we call homosexual," and he goes on to describe masturbation, oral sex, group sex, pornography, bondage and rape, pedophilia, etc...
The father finally asks, "So why did you want to know about 'a couple' and 'Sex'?"
"Oh, mummy said lunch would be ready in a couple of secs..."