Use your head!

use (one's) head

To use one's own intelligence and intellectual ability; to think logically and rationally. In this phrase, "head" refers to one's brain. Often said as an imperative. Come on, Dean, I know you can figure this out on your own. Use your head for a change! We'll have to use our heads if we're going to have any hope of solving this supply issue.
See also: head, use
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

Use your head!

and Use your noggin! and Use your noodle!
exclam. Think!; Think it through! You know the answer. Use your head! Use your noggin’, dogg!
See also: use
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.
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References in periodicals archive ?
Use your head! When you remind yourself that the source of your fright isn't real, the brain sends a calling message to the rest of your body.