What's "sex"?

A little girl runs to her father and asks him:
- Daddy, what's "sex"?
- OK, he thinks, this day was bound to come, and I am 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, wet dreams.
- Daddy, what is "a couple"?
And he carries on: a couple are the two people involved in the sex, but
this can be two males also, where they penetrate from the ass, or two
females which we call lesbians, where they use the tongue on the
vagina... and goes on to describe masturbation, oral sex, group sex,
pornography..
After he finishes, the father asks her:
So.. why did you want to know about "a couple" and "sex"?
-Oh, mummy said lunch would be ready in a couple of secs...

Thanks Marina!