Mental efforts depend significantly on the physical actions of an individual. Kahneman gives two practical illustrations of how the brain operates when an individual is momentarily at rest or mentally engaged. Principal among these tasks is observing the body activities when engaged in mathematical functions. Kahneman suggests that the eyes’ pupils will change as one contemplates on a challenge. He relates his findings to his personal experience at the University of Michigan, where he came across studies revealing the correlation of the pupils and mental engagement.