"Her other mouth" joke

A very naive British sailor is in a bar in London. He meets a wild girl, and she takes him upstairs. She takes off her pants and her panties.

He looks between her legs, and he says, "What's that?"

She says, "It's me lower mouth."

He says, "What do you mean,' your lower mouth?'"

She says, "Just what I said, it's me lower mouth. It's got a moustache... It's got lips..."

He asks, "Has it got a tongue in it?"

She says, "Not yet.. . "