In 16th-century France, the start of the new year was traditionally observed on April 1. Until 1562, when Pope Gregory introduced a new Christian calendar, the new year began on January 1. In France today, April 1 is called Poisson d'Avril .
French children fool their friends by taping a paper fish to their backs.
Some practical jokes are kept up the whole day or until the victim realizes what day it is. Most April Fool jokes are in good fun and not meant to do harm. The most clever April Fool joke is the one who prompts everyone to laugh, especially the person on whom the joke is played. The first of April is the day we remember what we are the other 364 days of the year. American humorist Mark Twain Laughter is used therapeutically by many hospitals and health care facilities.