If you see footage of penguins flying, check your calendar. There’s a good chance it’s April 1! The first day of April each year is celebrated as April Fools’ Day (sometimes called All Fools’ Day).

Although it’s not a legal holiday, April Fools’ Day is celebrated all around the world as a day filled with practical jokes and general silliness. You may want to be a little more cautious or skeptical on April 1, since family members, friends, neighbors, co-workers and even teachers may try to tickle your funny bone with a practical joke or a hoax of some kind.

So how did this tradition of craziness begin? In truth, it remains a mystery, although there are many theories about how April Fools’ Day got started.

Some believe the first association between April 1 and playing tricks can be found in Geoffrey Chaucer’s The Canterbury Tales from 1392. In “The Nun’s Priest’s Tale,” a fox tricks proud rooster Chauntecleer on syn March bigan thritty dayes and two.

Although Chaucer probably meant 32 days after March (May 2), many readers apparently misunderstood the line to mean March 32 — or April 1.

Others believe that April Fools’ Day was the result of a desire to celebrate the turning of the seasons around springtime. In fact, many cultures have historically held such celebrations around the beginning of April.

For example, the ancient Romans had a festival named Hilaria on March 25. The Hindus celebrate Holi, and the Jews celebrate Purim around this time of year.

Still others believe April Fools’ Day got its start because of the adoption of a new calendar in 1582. Many ancient cultures celebrated New Year’s Day around April 1.

In 1582, Pope Gregory XIII ordered the use of a new calendar, known as the Gregorian calendar, which celebrated New Year’s Day on January 1. According to legend, many people refused to recognize the new calendar or simply didn’t know about it. These people continued to celebrate New Year’s Day on April 1.

Eventually, other people began to make fun of these backward “fools” by sending them to look for things that did not exist (called a “fool’s errand”) or tricking them into believing something false.

Although we can’t really pinpoint how or when April Fools’ Day got its start, people the world over still celebrate it with glee year in and year out. Pranks can be quite simple, such as telling a friend his shoe is untied, or very elaborate, like some of the hoaxes described below.

Whatever the gag, it usually ends with the prankster yelling “April Fool!” when the victim falls for it. To give you a sense of how seriously some people take April Fools’ Day, here are three of the greatest April Fools’ Day hoaxes of all time:

• Swiss Spaghetti Trees — In 1957, the British Broadcasting Company (BBC) news program Panorama announced that Swiss farmers were harvesting a record spaghetti crop thanks to the elimination of the spaghetti weevil. News footage showed Swiss peasants pulling spaghetti from trees. Thousands of viewers were fooled. The BBC reported receiving many calls inquiring how to grow spaghetti trees!

• “Taco” Liberty Bell — In 1996, Taco Bell announced that it had bought the Liberty Bell to help ease the national deficit. When the company claimed it would be renaming it the Taco Liberty Bell, thousands of citizens were fooled and called to complain. The company revealed it was a practical joke a few hours later, but not before reporters asked White House press secretary Mike McCurry about the sale. Creating a joke of his own, he responded that the Lincoln Memorial had also been sold and would now be known as the Ford Lincoln Mercury Memorial!

• “Left-Handed” Whopper — In 1998, Burger King ran an advertisement in USA Today announcing its new “Left-Handed Whopper,” which was specifically designed for left-handed Americans by rotating all condiments exactly 180 degrees. Burger King revealed the hoax the next day but claimed that thousands of customers had requested the new sandwich at their restaurants!