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Fill in the blank: Something that happens once in a blue ___ happens very rarely.
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Moon
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Month
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Monday
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Moose
That's Correct!
It's Wrong!
The correct answer is "Moon". Something that happens once in a blue moon happens very rarely. The term "blue moon" refers to a second full moon occurring within a calendar month, which happens approximately once every 2.7 years. The phrase has since taken on a broader meaning to describe any event that is infrequent or unexpected.