When you speak of bad luck, it is said that one should always knock on wood. Also knocking when speaking of good luck apparently helps with having good luck. This is an old Celtic tradition related to belief of wood spirits.
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It's bad luck to leave a house through a different door than the one used to come into it.
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It is bad luck to put new shoes on a bed (or a table) (comes from the tradition of dressing a corpse in new clothes and shoes and laying them out so everyone can give their respects) - (UK)
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Opening an umbrella indoors is said to result in 21 days of bad luck. Some traditions hold that it is only bad luck if the umbrella is placed over the head of someone while indoors.
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Some motorcycle enthusiasts hang a biker's bell from a portion of their bike to protect themselves from evil road spirits.
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At times, a horseshoe may be found above doorways. When positioned like a regular 'U' it supposedly collects luck. However, when it is positioned like an upside-down 'U' the luck supposedly drains.
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Pirates believed that piercing the ears with such precious metals as silver and gold improved one's eyesight.
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A single magpie is considered a sign of bad luck. A Guide to the Scientific Knowledge of Things Familiar recites an old proverb concerning the incidence of bad weather when magpies forage alone and a possible scientific explanation for this.
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