A famous art collector was walking through the city when he noticed a mangy cat lapping milk from a saucer in the doorway of a store and did a double-take. He recognized the saucer was extremely old and very valuable, so he walked casually into the store and offered to buy the cat for $2.
The store owner replied, "I'm sorry, but the cat isn't for sale." The collector said, "Please, I need a hungry cat around the house to catch mice. I'll pay you $20 for that cat." The owner said, "Sold," and handed over the cat. The collector continued, "Hey, for the $20, I wonder if you could throw in that old saucer. The cat's used to it and it'll save me from having to get a dish."
The owner said, "Sorry buddy, but that's my lucky saucer. So far this week I've sold 68 cats." (from Cybersalt.org)