If idioms were literal.....
An idiom is an expression whose meaning is different from the words that make up the expression. It's raining cats and dogs, does not mean that cats and dogs are falling from the sky, but that there is a heavy rain.
paint the town - go out and enjoy an evening. To celebrate victories, teams painted the town red.
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time is running out - your deadline is approaching, your work is due
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saved by the bell - saved at the last minute