To think, especially in a careful or clever manner.
off the top of one's head
In an extemporaneous manner; without careful thought, preparation, or …
bright young thing
One who is youthful, clever, eager, and high-spirited in manner and at…
use one's head
To think carefully, especially as an alternative to being guided by on…
use a sledgehammer to crack a nut
To use disproportionate or significantly excessive force to carry out …
use in anger
Used for its intended purpose, as opposed to e.g. practice or testing