Pussy and bitch

A kid comes home from school and says to his mum, Mom I've got a problem.
OK. Tell me. Says his mum.
The boys at school are using two words I doesn’t understand.
So what are they?
Well, pussy and bitch. Says the boy.
Oh that’s no big deal. Pussy is a cat, and bitch is a female dog.
He thanks her and goes to visit dad in the garage. He says, Dad the boys at school are
using words I don't understand. I asked mum and I don’t think she told me the exact
meaning.
What are the words? He tells him...pussy and bitch.
Dad says, OK, and pulls a copy of Playboy down from the shelf, takes a marker and
circles the pubic area of the centrefold and says, Son, everything inside this circle is
pussy.
OK, dad, so what's a bitch?
Son, he says, everything outside that circle.