Prayer's little joke

Once upon a time, there was a man who was very interested in the cash register in the mall. Every time he enters the mall, he studies it. Once, he went to the mall to buy things, and the cashier went to another place to change money. He took the opportunity to put his hand under the scanner of the cash register and saw "Pig's trotters, 10 yuan" displayed on the computer screen. He was surprised to think that the cash register was broken, so he leaned his head over and looked at it. Later, the computer screen showed "pig head, 15 yuan"!