Terror keeps small prey alive, not broken. A snapped twig sends heart rate and blood pressure soaring, yet the same circuitry that ignites this alarm is wired to shut it down almost as fast. The sympathetic nervous system floods muscles with oxygen and glucose, while baroreflex loops and parasympathetic brakes move in behind the surge, forcing the spike to collapse once danger passes.
The real trick is that their bodies treat fear as a sprint, never a marathon. Short bursts of catecholamines and glucocorticoids mobilize fuel and sharpen sensory processing, but receptor desensitization and negative feedback in the hypothalamic pituitary adrenal axis cap the duration, limiting tissue damage and arrhythmia risk. Chronic activation would be lethal, so natural selection has filtered for individuals whose stress response is violently brief, then deeply off.
Still, these animals are not porcelain. Their myocardium is compact and efficient, arterial walls are elastic, and cardiac output can swing rapidly without structural failure. Many adopt behavioral tricks that outsource safety to the environment: tight cover, fixed paths, synchronized foraging. Each tactic reduces the baseline firing of the stress machinery, so when the forest explodes in noise, the system can afford to go to the edge again and again without burning out.
