I'm not sure!

But I did AI the origins of April fools day:

The exact origins of April Fools' Day are debated by historians, but several theories and historical events are commonly cited:

Calendar Change in France: The most popular theory links April Fools' Day to France in the 16th century. Prior to 1582, much of Europe, including France, celebrated the New Year around Easter, often beginning on March 25th and culminating on April 1st. In 1582, Pope Gregory XIII implemented the Gregorian calendar, which moved the start of the New Year to January 1st. News traveled slowly in those days, and some people either didn't hear about the change or resisted it, continuing to celebrate the New Year on April 1st. These individuals were often mocked and became the target of jokes and pranks, earning them the nickname "April Fools" or "poisson d'avril" (April fish) in France, referring to an easily caught fish.

Ancient Festivals: Some historians suggest connections to ancient festivals that involved merriment and trickery around the same time of year.

Hilaria (Ancient Rome): Celebrated on March 25th, this Roman festival involved people dressing in disguises and playfully mocking others.

Holi (Hindu Festival): This Hindu spring festival, celebrated in February-March, also involves playful mischief and a joyous atmosphere.

Vernal Equinox: Another idea is that the timing of April Fools' Day is related to the vernal equinox (around March 21st), a time when nature "fools" people with unpredictable weather changes.

Early Literary References:

Chaucer's "Nun's Priest's Tale" (1392): Some interpret a line in this work, "Syn March bigan, thritty dayes and two" (32 days after March began, i.e., April 1st), as an early reference to April fooling, though this is debated by scholars.

Flemish Poem by Eduard De Dene (1561): This poem describes a nobleman sending his servant on "fool's errands" on April 1st, which is considered one of the earliest clear references to the tradition.

Regardless of its precise origin, April Fools' Day became a popular tradition in Britain by the 18th century, spreading to other parts of the world. In Scotland, it evolved into a two-day event: "Huntigowk Day" (sending people on fool's errands) and "Tailie Day" (pinning tails or "kick me" signs on backs). Over time, it became common for pranks to only be permissible before midday on April 1st, with those pulling jokes after noon being labeled the "April Fool" themselves.