When an opossum plays dead, its heart rate plummets from 150 to just 12 beats per minute—a 92 percent drop.

The North American Virginia opossum (Didelphis virginiana) possesses a unique defense mechanism known as thanatosis or tonic immobility. Unlike a conscious choice to hide, this is a physiological collapse triggered by extreme fear. During this state, the animal's metabolic rate slows dramatically. Its heart rate drops by approximately 92 percent, falling from a normal resting rate of 150 beats per minute to just 12 beats per minute.This process is regulated by the autonomic nervous system, specifically through overstimulation of the parasympathetic system. Researchers at institutions like the National Wildlife Federation have documented that the state can last anywhere from a few minutes to four hours. While in this trance-like condition, the opossum's body temperature also drops slightly, further convincing predators that the animal is dead and potentially diseased.To enhance the illusion of death, the opossum's anal glands emit a green, putrid mucus. This chemical signal mimics the scent of cadaverine and putrescine—compounds naturally found in rotting flesh. Most predators, such as foxes and bobcats, are instinctively programmed to avoid eating carrion that smells rotten to prevent illness. This remarkable biological adaptation allows the opossum to survive encounters with much larger and faster predators.