A crash in the night or a car swerving into your lane can take over your body before you consciously register what happened. This episode breaks down that response, starting with Walter Bradford Cannon, who in 1914 and 1915 described how the sympathetic nervous system prepares animals for fighting or flight. Researchers now speak of the acute stress response and add freeze, fawn and flop to the list. The hosts explain how the sympathetic and parasympathetic systems work like an accelerator and a brake pressed at the same time, and how the amygdala, hypothalamus, pituitary and adrenal glands release adrenaline and cortisol.

The episode then gets to the stranger parts: bones releasing the hormone osteocalcin to hold off the brake, cortisol shutting down the immune system to save energy, and stress tilting perception so that a neutral text message reads like a threat. Animal studies show how often hiding beats bravery, and the hosts consider why people feel ashamed of freezing and how stress responses come up in self-defense law.

• Blood diverted from digestion, glucose dumped from the liver, faster clotting and dilated pupils
• The post-scare shakes as leftover muscular tension burns off
• A 2019 study by Clayton, Lang, Leshner and Quick in which anti-tobacco messages produced flight or fight reactions
• Lee Dugatkin’s guppies with a smallmouth bass: 40 percent of timid fish survived 60 hours and no bold ones did
• Thanatosis, rats that escape before fighting and cats that raise their fur to look bigger