Joke: Pussy And Bitch

A kid comes home from school and says to his mom, "Mom I've got a problem."
She says "Tell me." He tells her that the boys at school are using 2 words he doesn't understand. She asks him what they are.
He says "well, pussy¹ and bitch".
She says "Oh That's no big deal, pussy is a cat like our little Mittens², and bitch is a female dog like our Sandy."
He thanks her and goes to visit dad in the workshop in the basement. He says to his dad, "Dad the boys at school are using words I don't know, and I asked mom and I don't think she told me the exact meaning.
Dad says "Son, I told you never to go to mom with these matters, she cant³ handle them. What are the words?"
He tells him...pussy and bitch.
Dad says "OK" and pulls a Playboy down from the shelf, takes a marker and circles the pubic area of the centerfold and says, "son, everything inside this circle, is pussy."
"OK dad, so what's a bitch?"
"Son" he says, "everything outside that circle."