Riddle: What is the riddle?

There is a hotel in a city called "Difficult Hotel", and all the dishes ordered by customers can be satisfied. One day, a diner went to town to do business. At noon, he found a difficult hotel. Diners like to sip a few cups and order four kinds of snacks. The waiter wrote it down and left awkwardly. He immediately reported to the manager, who immediately found the chef. When the chef looked at it, the four dishes were Pipi, Skin Endothelium, Skin Lippi and Skin Peeling. The manager and chef are afraid of smashing the sign of "Difficult Hotel". After many twists and turns, they found an old chef who retired from his hometown and was over 60 years old, and solved the mystery. Readers, guess what these four dishes are. Answer: pig ears, pig belly, pig tongue and pig tail.