What’s That?

Aaron’s sitting on the toilet going pee-pee, and he looks down on himself as he goes.  Lillian is sitting nearby watching him, and he says, “What’s that?”
 
She:  What’s what?
Aaron:  That.
 
So she walks over to him to see what he’s pointing at.
 
She:  Oh, that’s your scrotum.
Aaron:  Scrotum?
She:  Yeah, your scrotum.
Aaron:  No, that’s balls.
She (with a smile):  Yeah, you’re right, those are your balls.
Aaron (with a smile):  Yeah, they’re our balls…