Grandad is out wandering around the garden one day and notices his grandson playing nearby. Grandad wanders over to see what's so fascinating. The little boy is trying, with all the diligence of youth, to put a worm back in its hole. The nature of worms being what they are, it is going everywhere but. Grandad tells the boy that if he can get that worm back in its hole, he'll get £5. The boy hops up and runs into the house.
He returns a moment later with a can of his sister's hairspray. He stretches the worm out, sprays it down, and voila! Right back into the hole.
Grandpa says "Well I'll be!" Fishes in his pocket, pulls out a £5 note and hands it to the boy. "Cor, thanks, grandad!" Granddad wanders off.
A bit later, grandad wanders back out to the garden. The boy is still out there playing. Grandad walks over, fishes a £10 note out of his pocket and hands it to the boy.
Confused, the boy says, "But grandad, you already gave me my £5."
Grandad smiles and says, "That is from your grandmother."