The fight-or-flight response, which was first identified by Harvard psychiatrist Walter Cannon in 1915, is a set of physical reactions you experience when you’re afraid. While the things that trigger the response vary based on your personal experience, the response itself is hard-wired into your body, activated when your autonomic nervous system and your pituitary gland ready your body to face danger.
In recent years, some scientists have proposed updating the term to ‘freeze, flight, fight or fright’ to fit the current understanding of how the response plays out. When you detect a predator, which is likely to hone in on motion, the instinctual first response is actually to freeze, with the hope it passes you by. The second-best option is fleeing the scene. Only when you’re attacked is fighting a good bet. Finally, playing dead through immobility – dubbed ‘fright’ – may lead the predator to loosen its grip enough to make an escape attempt.