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All answers having "Brains" as clue:

4 Character Answers:

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WITS



5 Character Answers:

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ASSET

GENII

SENSE



6 Character Answers:

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SMARTS



8 Character Answers:

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EGGHEADS

GENIUSES



9 Character Answers:

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EINSTEINS

INTELLECT

SMARTNESS



10 Character Answers:

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GRAYMATTER

GREYMATTER

INTELLECTS

MASTERMIND