(as) sharp as a whip
Very intelligent, clever, or quick-thinking. (A common but incorrect combination of the two phrases "sharp as a tack" and "smart as a whip.") Ted's as sharp as a whip, so he'll find a solution to this problem. Of course Ellen is our valedictorian—she's as sharp as a whip. My granddad may be old and cantankerous, but he's still sharp as a whip. You can't get anything past him.
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