Paddy and Mick are walking through the jungle. Paddy is carrying a telephone box on his back and Mick is carrying a huge anvil. After a while, Mick asks Paddy why he is carrying a telephone box.
"If a lion comes along," says Paddy, "I'll put the telephone box down, get inside and call for help"
"Not bad," says Mick.
Later, Paddy asks Mick why he is carrying an anvil.
"Simple," says Mick. "If a lion comes along, I'll drop the anvil and then I'll be able to run faster."