Once a wedding ring has been placed on the finger, it is considered bad luck to remove it.
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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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Placing keys on a table is considered unlucky. (Sweden)
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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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In some parts of England, rum is used to wash a baby's head for good luck.
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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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An acorn should be carried to bring luck and ensure a long life.
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Placing a hat on the bed is, apparently, bad luck. (South Carolina)
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