What is the festival two days before the Cold Food Festival?

The Cold Food Festival, also known as "Smoke-free Festival", "Cold Food Festival" and "Hundred Days Festival", is held on April 3rd, that is, from the winter of the summer calendar to the future/0/05 day, one or two days before Tomb-Sweeping Day. Then, the festival two days before the Cold Food Festival is April Fool's Day (April 1), which is a traditional folk festival in western society. On this day, people play jokes on people around them in various ways. When they are told that it is April Fool's Day, they suddenly realize.