Examples of Newton's third law of motion are ubiquitous in everyday life. For example, when you jump, your legs apply a force to the ground, and the ground applies and equal and opposite reaction force that propels you into the air. Engineers apply Newton's third law when designing rockets and other projectile devices.
His fight or flight is being activated making the adrenaline go through him making him alert and ready for what's coming at him. Depending on what happens next Fight or Flight will take place. If the body feels in danger he will flee and if the body thinks it's not as big of a threat he can fight it off.
