There once was a little boy who was celebrating his 11th birthday.
He decided to test his family to see if they remembered his birthday, so he goes downstairs to his father. "Betcha can't guess how old I am today", the boy said.
The father has no clue and finally gives up. "I'm eleven!" the boy exclaims.
Next he goes in the kitchen, walks up to his grandma. Betcha can't guess how old I am today".
"Let me give it a guess", Grandma says as she sticks her hand in his trousers.
She plays with his testicles for a minute or so (squeezing them, moving them back and forth), takes her hand out of his trousers, and says, "Your eleven years old".
"How did you know?", the boy asked.
Grandma replied, "I heard you tell your father".