A man walked into a curio shop and began to browse. He was attracted to a brass rat on a shelf behind the counter. He asked the shopkeeper for a price, and was told to make an offer. Presently they agreed on a price, and the brass rat changed hands. The shopkeeper warned the customer as he took the money, "This sale is final. If you leave the shop with the brass rat, I won't take it back under any circumstances."

The customer agreed and left with the rat. As he walked home, he noticed that a live rat came scurrying out of an alley and began to follow him. Soon there were more, all following him and milling bout his feet. The man began to run, but the rats kept up, and more joined the procession. After a few minutes, thousands of rats were chasing after the man. The man ran frantically for the river, and threw the brass rat into the water. The live rats followed the brass rat, and soon all had drowned. The man returned to the curio shop, and on seeing him enter, the shopkeeper shouted, "I told you, the sale was final! You cannot return the brass rat!" The customer replied, "That's no problem. I just wondered if you had a brass lawyer in stock."