On April 1st in France, people play tricks on their friends, teachers, etc… one of children’s favourite tricks being to hang paper fish onto people’s backs. You can also tell them an unlikely story and shout “Poisson d’avril” at the end, to acknowledge it’s a prank.
A year ago I made this mosaic, composed of fish photos, real or made of stone, taken in Paris or elsewhere, and posted it on flickr on April 1st
Poisson d’avril ! One man’s fish is another man’s poisson!