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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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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An acorn at the window will keep lightning out
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The superstitious symbolism of a black cat crossing one's path is dependent upon culture: some cultures consider this a sign of impending bad luck, while some cultures consider this a sign of impending good luck.
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Once a wedding ring has been placed on the finger, it is considered bad luck to remove it.
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Placing keys on a table is considered unlucky. (Sweden)
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Placing a hat on the bed is, apparently, bad luck. (South Carolina)
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