A boy is eating breakfast with his grandfather one morning, and
 the grandfather notices the boy playing with some kind of chemical
 in a test tube.
 
 The boy pours the chemical on a worm and the worm turned hard as a
 rock. The grandfather says, "Son, what is that you're putting on
 that worm?" 
 
 The boy replies, "I'm not sure. Something I mixed up. But
 everything I put it on turns hard."
 
 So the grandfather says, "I'll make a deal with you...let me
 borrow some of that, and if it does what I think it will do, I'll
 leave you £5 on your breakfast plate in the morning."
 
 The boy says OK, and goes off to school. The next morning when the
 boy went down for breakfast he had £25 on his plate. He says,
 "Grandpa, I thought you said you would leave me £5 if that stuff
 did what you thought it would do."
 
 The grandfather replies, "I did, son....the other £20 is from
 Grandma!"