A cavity is an empty space waiting to be filled with dentist bills.
An elderly lady lost her handbag in the bustle of Christmas shopping. It was found by an honest little boy who returned it to her. Looking in her purse, she commented, “That’s funny. When I lost my bag there was a $100 bill in it. Now there are 100, $1 bills.” The boy quickly replied, “That’s right, lady. The last time I found a lady’s purse, she didn’t have any change for a reward.”