A boy says to his dad: "how old do you think I am today?"
Dad: "I dont know"
Boy: "Eleven"
He then goes into the next room and says to his Grandma: " Guess 
how old I am?"
His grandma puts her hand down his trousers and fondles with his
genitals.
After a few minutes she says: "Eleven"
Boy: " How did you know"
Grandma: "I heard you tell your father"