On April the first, better watch your back!

On Wednesday this week, you may end up with a paper fish pinned to your back. This is how children in France celebrate "April Fool's Day," a worldwide tradition the French claim to have originated.

The story begins long ago. In 1564, French King Charles IX reformed the calendar and moved the start of the year from the end of March to the first of January. Despite the royal decree, many people did not accept the change and maintained the old tradition of celebrating the New Year during the week of the spring equinox, when night and day are of equal length. Rejoicing at the promises of spring, they would exchange greetings and gifts, often in the form of food.

These "traditionalists" were considered backward fools who stubbornly clung to the "old ways." They were mocked, and pranksters would play tricks on them such as attaching fake food, mud cakes, or paper fish to their backs. This is the origin of the "Poisson d'avril"—the French equivalent of "April Fool's."

Five centuries later, teachers, parents and figures of authority still fall prey to "poissons d'avril." In the 1960s, it was popular to broadcast outrageous news on French national television on this day. One of these pranks drew quite a lot of laughs from viewers: it was announced that a law would soon be passed prohibiting smoking in public places. A really good "poisson d'avril" has to be plausible and convincing though, and this one, some 40 years ago, wasn't either.