Some historians speculate that April Fools' Day dates back to 1582, when France switched from the JULIAN calendar to the GREGORIAN calendar, as called for by the Counsel of Trent in 1563. In the Julian calendar, as in the Hindu calendar, the new year began with the spring equinox around April 1.  People who were slow to get the news or failed to recognize that the start of the new year had moved to January 1 and continued to celebrate it during the last week of March through April 1 became the butt of jokes and hoaxes and were called "April fools." These pranks included having paper fish placed on their backs and being referred to as poisson d'avril" (April fish), said to symbolize a young, easily caught fish and a gullible person. April Fools'Day spread throughout Britain during the 18th century. In Scotland, the tradition became a two-day event, starting with "hunting the gowk," in which people were sent on phony errands (gowk is the word for cuckoo bird, a symbol for fool)and followed by Tailie Day, which involves pranks played on people's derrieres, such as pinning fake tails or "kick me" signs on them.