At the first of the month, you may notice people saying “rabbit rabbit." That’s because of a superstition that if your first words that day are “rabbit rabbit,” you’ll have luck for the rest of the month.

Alleged followers of this tradition have included actress Sarah Jessica Parker and President Franklin Delano Roosevelt, who also carried a rabbit’s foot for good luck.

The earliest written reference behind why people started saying “rabbit rabbit” (or variations like “rabbits” or “bunny bunny”) may be a 1909 issue of the British journal Notes and Queries, in which a parent observed that some children said “rabbits” on the first of every month for good luck.

After that, references to the superstition only popped up occasionally. In 1935, the British Nottingham Evening Post reported this bit of gossip: “Mr. Roosevelt, the President of the United States, has confessed to a friend that he says ‘Rabbits’ on the first of every month—and, what is more, he would not think of omitting the utterance on any account.”

The superstition also appeared in Trixie Belden’s The Mystery of the Emeralds, a 1962 book in the kids’ mystery series, and on Nickelodeon in the 1990s.

Some have suggested “rabbit rabbit” is considered lucky because rabbits are notoriously fertile and heavily associated with spring and renewal. But the fact is, we have no idea why people say “rabbit rabbit”—or whether it’s related to the superstitions around rabbit’s feet.

And why, exactly, do people carry around rabbits' feet for luck? One theory is that European Americans appropriated rabbits’ feet from African American customs or jokes they didn’t fully understand, writes Bill Ellis in his book Lucifer Ascending: The Occult in Folklore and Popular Culture. He explains that in the early 20th century, U.S. companies that sold rabbits’ feet vouched for their authenticity by claiming that a Black person had cut them off under specific, unlucky-seeming conditions.

“A 1908 British account reports rabbits’ feet imported from America being advertised as ‘the left hind foot of a rabbit killed in a country churchyard at midnight, during the dark of the moon, on Friday the 13th of the month, by a cross-eyed, left-handed, red-headed bow-legged Negro riding a white horse,’” he writes. “While other collected versions disagree about exactly when the rabbit must be killed, all indicate that the rabbit's foot historicizes an especially uncanny or evil time: the dark of the moon; a Friday; a rainy Friday; a Friday the Thirteenth.”

It’s hard to say whether these marketing descriptions reference a real tradition, a joke among African Americans or a cruel joke about African Americans (at least one marketing description for a rabbit’s foot used a racist slur). But it is true that other superstitions about body parts can be found among early European and African Americans, as well as in Europe and Africa. Benjamin Radford, deputy editor of Skeptical Inquirer, suggests the rabbit’s foot could be connected to a European good luck charm called the Hand of Glory.

“The Hand of Glory was a hand cut from a hanged man,” he says. In medieval Europe, authorities sometimes left hanged men’s bodies out in public to warn others against committing crimes; “but oftentimes, people would go and cut off one of the hands…usually the left one, and pickle it.”

Like the Hand of Glory, Ellis writes that rabbit’s feet were sometimes considered lucky because of their association with the body of a criminal. According to the early 20th-century folklorist Newbell Niles Puckett, Grover Cleveland was said to have received the foot of a rabbit killed on the grave of Jesse James when Cleveland was running for president in 1884.

Writing about this more than 50 years later, Puckett observed: “the more wicked the person who is dead, the more effective the charm associated with his remains."

And even though many assume these traditions must stretch far back in time, there are no written records of either the rabbit’s foot or the “rabbit rabbit” superstition before the 20th century.

“There’s a lot of superstitions, customs and beliefs that we sort of take for granted and we assume are centuries-old,” Radford says, but “in many cases are relatively new."