The familiar phrase “playing possum” describes the defensive behavior of the Virginia opossum, which appears suddenly lifeless when threatened. The opossum is not actually “passing out” in the medical sense, but rather enters a profound, involuntary state of shock. This reaction is a last-resort survival strategy, and it is not a conscious decision made by the animal to fake its own death.
The Mechanism of Tonic Immobility
The opossum’s catatonic state is scientifically termed thanatosis, or tonic immobility. This reflex action is triggered by a sudden surge of overwhelming fear or extreme stress. The reaction is managed by the autonomic nervous system, which governs involuntary body functions.
When this defensive mechanism is activated, the opossum’s physiology undergoes a significant change. During this episode, the animal’s heart rate can decrease by as much as 46% from its normal pace. Simultaneously, the respiratory rate slows significantly, sometimes dropping by nearly a third, making the possum’s breathing appear shallow or even imperceptible.
The body temperature also drops slightly, contributing to the illusion of a recently deceased animal. Although the opossum appears completely unresponsive and comatose, its brain remains active. This awareness distinguishes tonic immobility from true unconsciousness, as the opossum is internally monitoring the situation for any sign that the threat has departed.
Observable Features of the Feigned State
The opossum’s performance of feigned death is convincing because of several external signs that mimic decomposition. The animal typically collapses and lies motionless on its side, with its body becoming rigid and its feet curling inward. Its mouth usually hangs open, often accompanied by drooling or a loll of the tongue, giving the impression of a final gasp.
To enhance the illusion of a decaying carcass, the opossum’s eyes may remain fixed in a glassy stare or be closed. The most persuasive element is the release of a foul-smelling, greenish fluid from the animal’s anal glands. This putrid scent is intended to repel predators, as most instinctively avoid eating something that smells as though it has been dead for some time.
The Trigger, Duration, and Recovery
The trigger for tonic immobility is an inescapable threat, often initiated by physical contact or violent confrontation. This forces the marsupial into a frozen, unresponsive posture. This response is reserved for moments when other defenses, like hissing or baring its fifty teeth, have failed to deter an attacker.
The duration of this catatonic state directly relates to the level of perceived danger. An opossum may remain immobile for only a few minutes if the threat quickly passes, but the state can persist for as long as four hours in intense situations. During this time, the opossum’s body will not react to prodding or other external stimulation, maintaining the death facade.
Recovery is a gradual process that begins once the opossum senses that the danger has vanished and it is safe to move. The first indication of returning awareness is often a slight twitching of the ears, followed by slow, cautious movement. The animal rises and quickly leaves the area only after it is certain the predator is no longer present.