He knows 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 20 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 it and it'll save me
from having to get a dish."
The owner says, "Sorry buddy, but that's my lucky saucer. So far this
week I've sold sixty-eight cats."