A little girl runs out to the backyard where her father is working, and asks him, "Daddy, what's sex?"
Her father sits her down, and tells her all about the birds and the bees. He tells her about conception, sexual intercourse, sperms and eggs. He goes on to tell her about puberty, menstruation, erections, wet-dreams...and he thinks, what the hell, and goes on to tell her the works.
He covers a wide and varied assortment of sub topics and by the time he's finished, his daughter is somewhat awestruck with this sudden influx of bizarre new knowledge. Her father finally asks: "So what did you want to know about sex for?"
"Oh, mommy said to tell you lunch would be ready in a couple of secs..."