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 shop.
He does a double take, as he notices that the saucer is extremely old and very valuable. He walks casually into the shop
The shop owner 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 pounds for that cat."
And the owner says "Sold," and hands over the cat.
The collector continues, "Hey, for the twenty pounds I wonder if you could throw in that old saucer. The cat's used to it and it'll save me having to get a dish."
And the owner says, "Sorry paly, but that's my lucky saucer. So far this week I've sold sixty-eight cats."