In sixteenth-century France, the start of the new year was observed on April first. It was celebrated in much the same way as it is today with parties and dancing into the late hours of the night. Then in 1562, Pope（罗马教皇）Gregory introduced a new calendar for the Christian world, and the new year fell on January first. There were some people, however, who hadn't heard or didn't believe the change in the date, so they continued to celebrate New Year's Day on April first. Others played tricks on them and called them "April fools." They sent them on a "fool's errand" or tried to make them believe that something false was true. In France today, April first is called "Poisson d'Avril." French children fool their friends by taping a paper fish to their friends' backs. When the "young fool" discovers this trick, the prankster（爱开玩笑的人）yells "Poisson d'Avril!" (April Fish!)
Today Americans play small tricks on friends and strangers alike on the first of April. One common trick on April Fool's Day, or All Fool's Day, is pointing down to a friend's shoe and saying, "Your shoelace is untied." Teachers in the nineteenth century used to say to pupils, "Look! A flock of geese!" and point up. School children might tell a classmate that school has been canceled. Whatever the trick, if the innocent victim falls for the joke the prankster yells, "April Fool! "
The "fools' errands" we play on people are practical jokes. Putting salt in the sugar bowl for the next person is not a nice trick to play on a stranger. College students set their clocks an hour behind, so their roommates show up to the wrong class - or not at all. Some practical jokes are kept up the whole day before the victim realizes what day it is. Most April Fool jokes are in good fun and not meant to harm anyone. The most clever April Fool joke is the one where everyone laughs, especially the person upon whom the joke is played.