Ask a joke about counterfeiting

There is a person who specializes in making counterfeit money. He thinks that city people are too smart and counterfeit money is easy to be seen through. He decided to use these counterfeit banknotes in the mountains. One day, he bought a pack of cigarettes with 3 yuan money in a small shop in the mountains. He took out 10 yuan counterfeit money, and the shopkeeper gave him a 3 yuan and a 4 yuan bill. Soon he used up thousands of counterfeit notes. Take back a bag full of money when you leave. When I got home, my wife opened it and found all the money from 3 yuan and 4 yuan.