Friday 13th Common But Silly Superstitions

No umbrellas inside

 And not just because you'll poke someone's eye out. Opening an umbrella indoors is supposed to bring bad luck, though the origins of this belief are murky. Legends abound, from a story of an ancient Roman woman who happened to have opened her umbrella moments before her house collapsed, to the tale of a British prince who accepted two umbrellas from a visiting king and died within months. Like the "don't walk under a ladder" superstition, this seems to be a case of a myth arising to keep people from doing something that is slightly dangerous in the first place.

Cross your fingers

Those wishing for luck will often cross one finger over another, a gesture that's said to date back to early Christianity. The story goes that two people used to cross index fingers when making a wish, a symbol of support from a friend to the person making the wish. (Anything associated with the shape of the Christian cross was thought to  be good luck.) The tradition gradually became something people could do on their own; these days, just saying "fingers crossed" is enough to get the message, well, across.

666

Three sixes in a row give some people the chills. It's a superstition that harks back to the Bible. In the Book of Revelation, 666 is given as the number of the "beast," and is often interpreted as the mark of Satan and a sign of the end times.

According to State University of New York at Buffalo anthropologist Philips Stevens, the writer of Revelation was writing to persecuted Christians in code, so the numbers and names in the book are contemporary references. Three sixes in a row is probably the numeric equivalent of the Hebrew letters for the first-century Roman Emperor Nero. [End of the World? Top Doomsday Fears]

Don't walk under that ladder!

Frankly, this superstition is pretty practical. Who wants to be responsible for stumbling and knocking a carpenter off his perch? But one theory holds that this superstition arises from a Christian belief in the Holy Trinity: Since a ladder leaning against a wall forms a triangle, "breaking" that triangle was blasphemous.

Then again, another popular theory is that a fear of walking under a ladder has to do with its resemblance to a medieval gallows. We're sticking with the safety-first explanation for this one.

Careful with that mirror

According to folklore, breaking a mirror is a surefire way to doom yourself to seven years of bad luck. The superstition seems to arise from the belief that mirrors don't just reflect your image; they hold bits of your soul. That belief led people in the old days of the American South to cover mirrors in a house when someone died, lest their soul be trapped inside.

Like the number three, the number seven is often associated with luck. Seven years is a long time to be unlucky, which may be why people have come up with counter-measures to free themselves after breaking a mirror. These include touching a piece of the broken mirror to a tombstone or grinding the mirror shards into powder.