Another Friday the 13th is almost upon us, and it will inevitably raise fears of bad luck in some people. It's 2015; we have satellites in orbit, we can talk live on small portable devices between nearly any two points on Earth, and we can see more cat videos in one day than our forefathers could have dared dream of.

It's the age of science, yet ancient superstitions still have a hold on us. Many superstitions seem insignificant or even silly -- who really cares if you avoid a black cat's path? There is a fine, and sometimes downright blurry, line between superstition, myth and urban legend. But not all superstitions are harmless.

In some places, people believe that the body parts of albinos can bring them good luck. In the East African countries of Tanzania and Burundi, dozens of albinos have been murdered for this reason since 2008, according to the Red Cross. Superstition has also contributed to the decline of some of the world's most magnificent animals: Several species of rhinos have been driven to near extinction because of demand for their horns, claimed to act as an aphrodisiac or even cure cancer.

Superstitions often take the form of taboos, things you shouldn't do. In some cases the superstition comes with its own remedy or counter-charm, its own mystical method for undoing the harm. For example, if you spill salt on a table that's bad luck, but you can avert tragedy by throwing the salt over your left shoulder. In that spirit, here are 13 things you should never do on Friday the 13th. Some of these are familiar -- others are obscure relics from bygone days.

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One old superstition cautions against opening an umbrella inside a house. To do otherwise invites back luck, either upon the umbrella opener or upon the household. It's not clear where this idea came from, though sources note that early umbrellas opened using a tight spring which wasn't reliable and could be dangerous if a finger was caught in it, or the umbrella opened suddenly or unexpectedly. In addition to being a common superstition, it's also practical advice: You don't need an umbrella inside, and getting a fully-opened umbrella through a door can be difficult.

It's one of many admonitions against doing something mildly disruptive or destructive and unnecessary, such as breaking a mirror or walking under a ladder: It's probably harmless, but easily avoided by paying attention.

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If you want to keep from going prematurely gray (or white), avoid sudden fear or shock, which has been said to cause hair to turn white overnight. For centuries, it was believed that people who have terrifying experiences with ghosts or brushes with death find that their hair has turned white. However this is medically impossible. There's no mechanism by which hair can spontaneously turn white, either suddenly or overnight.

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“O swear not by the moon, the inconstant moon, That monthly changes in her circled orb, Lest that thy love prove likewise variable." So says Juliet Capulet in Shakespeare's most famous tragedy. Why shouldn't lovers swear their devotion under a romantic moon? Because centuries ago the moon was considered erratic and unreliable, since it changes shape and size throughout the month -- not to mention completely disappearing on rare occasions during eclipses!

Love vowed under the moon was thought to be just as transient as the moon itself.

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If you must yawn, always cover your mouth. It's good manners, and if you don't -- according to superstition -- it could lead to illness or even demonic possession. In the “Giant Book of Superstitions" author Claudia de Lys explains: “In the Middle Ages, it was a common belief that yawning was brought about by the Devil, who watched for his chance to enter the body through the mouth and take possession of a man or woman. The counter charm was to make the sign of the cross over the mouth so Satan could not enter." The cross over the mouth later became simplified into simply covering the mouth.

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On Friday the 13th, or any other day, you must not cross a knife and a fork on a dinner table. Not only is it improper etiquette but you will invite bad luck because it symbolizes difficult times ahead. Another superstition held that a knife presented as a gift should never be given outright to the recipient but instead either bought or loaned. You should ask for a token payment, perhaps a nickel or penny, lest the knife represent a severing of the bonds of friendship.

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It should be obvious, but seating 13 people at a dinner table is never a good idea. Not only will the first person be done eating by the time the last person is served, but it's extremely unlucky. The origins of this superstition are not hard to fathom, coming from the book of John in the Bible, in which Jesus Christ was betrayed by Judas -- the 13th guest at his table. The unluckiness of 13 goes beyond just a table; many believe that if 13 people meet in a room, one of them will die within the year.

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If you have a date planned for Friday night, cancel it. An old English superstition holds that any courtship undertaken on a Friday is doomed. Not only that, but neighbors and friends who saw a young couple out on a Friday were expected to harass them by beating loudly on pots and pans to shame them into delaying their courtship until the following day. This was part of a larger phenomenon of social control called chivaree, a form of community censure which embarrassed people into acting according to proper custom.

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Most people know that breaking a mirror is said to bring seven years bad luck, but you may not know that mirrors must also be covered up in the presence of the sick or dying. This is because, by some traditions, the patient may happen to look in the mirror and see Death itself lurking in the reflection.

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If you're a woman on a boat or a ship, your very presence may endanger the crew, according to old marine superstitions. A woman who boards a ship, even temporarily, may prophecy a watery doom. Fishing (and, by extension, seafaring) has traditionally been considered dirty, dangerous work unsuitable for the fairer sex, and may have led to this sexist superstition.

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Speaking of weird fishermen's superstitions, according to Iona Opie and Moira Tatem's “Dictionary of Superstitions," there is one fish That Shall Not Be Named. Sometimes it was called “the beast," other times “the red fish," “the foul fish," or simply “the fish." Scientists may call it Oncorhynchus gorbuscha, or even Salmo salar, but under no circumstances should the fish be called by its true name: salmon.

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If you happen to be on a boat at sea accompanied by a woman (especially one who says the word “salmon" aloud) you're clearly in trouble. But not as much trouble as someone who falls overboard, because of a strong superstition against saving the life of a drowning person.

The roots of this superstition are thought to come from the idea that a drowning person's death is the sea's (or God's) will, and by saving the person, the rescuer is thwarting the natural order of things. Bodies of water, including oceans and rivers, were believed to demand a certain number of human lives each year.

If a person is going under for the third time (another common superstition) it's because the sea wants a human life, and if you prevent it from taking that life, you yourself will soon drown. Throughout history many thousands of people have likely died because superstitious bystanders believed this myth.

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It's unlucky to get into bed on one side and get up the next morning on the other side of the bed. This of course poses a problem if one side of your bed is against a wall, though presumably you could exit at the foot of the bed. Though the superstition sounds silly to modern ears, it's why we say that a person who's in a bad mood “got up on the wrong side of the bed."

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Another thing you should never do -- and certainly not on a Friday the 13th -- is burn eggshells. This applies to the person cooking at home, or even a camper carelessly tossing eggshells into a campfire. This superstition is only indirectly unlucky to the person who commits the offense. Instead it was believed that burning the eggshells caused burns to the nether regions of the hen that laid that egg, resulting in an (understandable) refusal to lay more eggs.