By contrast, people who are defensive or angry may protectively fold their arms across their chest, clench their hands into a fist or tightly grip their arm or wrist.

FORBES: Body Language Savvy for Sales

Both techniques were able to see the brain acting to clench a volunteer's fist in his dream in exactly the way that it does when ordering fist-clenching in reality.

ECONOMIST: Reading the brain

This action was to clench either their right or their left hand into a fist.

ECONOMIST: Reading the brain