"Women got teeth down there" joke

A little boy is waiting for his mum to come out of the changing room in a department store and gets a bit bored so decides to have a look around.
When she comes out of the changing room she finds him with his hand up a dummy's skirt. "GET YOUR HAND OUT OF THERE," she shouts. "DON'T YOU KNOW WOMEN HAVE GOT TEETH DOWN THERE."
The little boy snatches his hand away and thanks his lucky stars that nothing serious happened.
So all his life this poor lad grows up thinking that women have got teeth down below.
When he reaches 16 he gets himself a girlfriend. One night her parents go out so she invites him round. After a few hours of snogging on the sofa she asks him if he want's to go a bit further. "What do you mean?" he asks.
"Well, why don't you put your hand down there?" and points to her privates.
"Good god no!" He cries, "You've got teeth down there."
"No I haven't."
"Yes you have; my Mum told me."
"No I haven't. LOOK!" With that she takes off her trousers and gives him a little peek.
"No, sorry," he says" MY MUM TOLD ME!"
"Oh, for goodness sake!" she screams and with that whips off her knickers, sticks her legs behind her head and says, "Look I haven't got any teeth down there."
He replies, "Well, with the state of those gums, I'm not surprised!