If Friday the 13th is troubling you, here are 12 other superstitions you might want to worry about.

1. A single magpie is "one for sorrow".

2. Don't open umbrellas indoors, at least if you don't want to upset the sun gods.

3. Don't walk under a ladder. A leaning ladder supposedly represents the trinity – walk right through it, and you're in league with the devil.

4. Stay away from this number in parts of China. Four sounds like "death" in Cantonese and in Hong Kong. Some high-rise buildings don't have fourth, 14th or 40th floors. A study published in the Medical Journal of Australia to find if "psychological stress engendered by fear of the number four" led to more cardiac deaths among Hong Kong Chinese people on the 4th, 14th of 24th of the month, however, found no correlation.

5. The evil eye: strolling through a Turkish market, you'll see vivid blue evil-eye pendants to ward off the bad luck.

6. Don't wear opal, at least if you fear it is contaminated with evil. This superstition came about in the 19th century: Sir Walter Scott's character Lady Hermione in Anne of Geierstein turns to ashes after holy water is sprinkled on her opal-bedazzled hair.

7. It is seven years' bad luck if you break a mirror. The Romans are said to have believed that life renews itself every seven years, so breaking a mirror disrupted that link to your inner self.

8. Flight 666 to HEL. A Finnair flight from Copenhagen to Helsinki, which flies on Fridays – including those with a 13 next to them. Last Friday the 13th, the flight was full.

9. This number sounds like "suffering" (kyū) in Japan and is considered unlucky. Certain planes on All Nippon Airways omit row nine (and four, and 13).

10. Don't spill salt. A famous depiction is Leonardo da Vinci's Last Supper, where Judas's spilling of it is associated with treachery and lies.

11. Walk away from that black cat. It's evil. Cats were believed to be the familiars of witches in the middle ages.

12. The number 13 has its own named phobia: friggatriskaidekaphobia. Mark Twain was once the 13th guest at a dinner ("It was bad luck," he said. "There was only food for 12."), Buckingham Palace was bombed by the Luftwaffe on Friday 13 September 1940, and Alfred Hitchcock, perhaps fittingly, was born on Friday 13 August 1899.