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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There are numerous sailors' superstitions, such as: it is considered bad luck for a ship to set sail on a Friday, to bring anything blue aboard, to stick a knife into the deck, to leave a hatch cover upside-down, to say "pig", or to eat walnuts aboard.
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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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Placing keys on a table is considered unlucky. (Sweden)
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If you catch a falling leaf on the first day of autumn you will not catch a cold all winter.
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An acorn at the window will keep lightning out
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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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Pirates believed that piercing the ears with such precious metals as silver and gold improved one's eyesight.
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