A famous art collector is walking through the city when he notices a mangy
cat lapping milk from a saucer in the doorway of a store and he does a
double take. He recognizes that the saucer is extremely old and very
valuable, so he walks casually into the store and offers to buy the cat
for two dollars.
The storeowner replies "I'm sorry, but the cat isn't for sale.
The collector says, "Please, I need a hungry cat around the house to catch
mice. I'll pay you twenty dollars for that cat."
And the owner says "Sold," and hands over the cat.
The collector continues, "Hey, for the twenty bucks I wonder if you could
throw in that old saucer. The cat's used to eat and it'll save me from
having to get a dish."
And the owner says, "Sorry buddy, but that's my lucky saucer. So far this
week I've sold sixty-eight cats."