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  • Imagine you're being attacked by a ferocious predator.

  • With no chance of escape, you do what any courageous, self-respecting possum would do:

  • curl into an immobile state called catatonia, stick out your tongue, drool, and ooze some foul-smelling liquid from your anal glands.

  • Disgusted, your assailant loosens its grip, decides you're not the dinner it was looking for, and departs.

  • After 10 minutes, you resurrect and merrily saunter on.

  • From lemurs to lizards, ants to amphibians, sharks to chickens, hundreds of animals "play dead" as a survival tactic.

  • Nicknamed "playing possum" after its star performer, feigning death is also called thanatosis.

  • That's from Thanatos, the ancient Greek deity of death.

  • But most scientists call it tonic immobility, or TI.

  • How and why TI occurs depends on the species and situation.

  • Spewing stench and adopting odd postures are common and often play important roles.

  • Other animals sacrifice their neighbors: quail chicks that freeze while their kin run amok have a better chance of survival when pursued by a cat.

  • Speaking of cats, feline mothers can pinch the napes of their kittens' necks and induce another kind of immobility called clipnosis.

  • This keeps their kittens quiet and easy to transport.

  • Most of the physiological mechanisms underlying these theatrics originate in the parasympathetic nervous system, better known for controlling cycles of resting and digesting.

  • In possums, the parasympathetic nervous system causes their heart rates to drop by nearly half, respiration by a third, and body temperatures by more than half a degree Celsius for up to an hour.

  • The neurotransmitter dopamine also plays a part.

  • Flour beetles with low dopamine levels, play dead more frequently than those with high levels.

  • And anything blocking dopamine receptor sites can lengthen catatonia.

  • But maintaining a death ruse isn't easy.

  • The performers are constantly gauging their surroundings for queues on when it's safe to rise.

  • Chickens, for instance, can sense when a predator's eyes are upon them.

  • Researchers know this, because when they used a stuffed hawk in an experiment, their chicken subjects came out of their catatonia quicker when the hawk's eyes were averted.

  • Other animals use TI for purposes other than defense.

  • When the sleeper cichlid feels peckish, it sinks to the lake floor and lies motionless.

  • Its splotchy coloration making it seem like a rotting carcass.

  • If a small scavenger investigates, this undead trickster strikes.

  • Some animals even feign death as a sexual ploy.

  • Male nursery spiders offer gifts of silk-wrapped insects in hopes of wooing females.

  • But those females are known to eat love-seeking males.

  • By playing dead while the female eagerly devours her snack, these males can cautiously revive and improve their chances of successfully mating.

  • So TI can work to an animal's advantage, unless someone else knows its secret.

  • California orcas can flip over young great white sharks, inducing TI for so long the immobilized sharkswho must move to respireessentially suffocate.

  • Humans can also flip sharks into TI.

  • By stroking a shark's electrically-sensitive snout and gently turning it over, researchers can induce TI that lasts up to 15 minutes.

  • That's enough time to insert tags, remove hooks, and even perform surgeries.

  • There are risks however:

  • TI can hamper respiration and induce hyperglycemia, a sign of stress.

  • So this technique should only be used when necessary.

  • Humans can also experience TI when they freeze with fear during violent assaults.

  • Recognizing this ancient, involuntary form of self-defense has significant implications when trying to understand why some victims don't flee or fight in the face of danger.

  • So, studying TI in non-human animals not only helps us better understand some odd behaviors, it can also help us better understand our own, sometimes counterintuitive, responses to violence.

  • Love animals? Check out this playlist for more videos on some of our favorite furry and not-so-furry friends.

Imagine you're being attacked by a ferocious predator.

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C1 US TED-Ed dopamine parasympathetic death dead possum

The surprising reasons animals play dead - Tierney Thys

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    April Lu posted on 2018/04/19
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