Apparent death

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"Playing possum" redirects here. For the 1975 album by Carly Simon, see Playing Possum.

Apparent death, colloquially known as playing dead or playing possum, is a behavior in which an animal takes on the appearance of being dead. This form of animal deception is an adaptive behavior also known as tonic immobility or thanatosis. Apparent death can be used as a defense mechanism or as a form of aggressive mimicry, and occurs in a wide range of animals.

When induced by humans, the state is sometimes colloquially known as animal hypnosis. According to Gilman et al.,[1] the investigation of "animal hypnosis" dates back to the year 1646 in a report by Kircher.


The term "thanatopsis" (Greek: opsis "a sight, view") may be more correct that "thanatosis" which simply refers to death. The addition of the term "-opsis" lends the meaning that the animal only appears to be dead but is, in fact, alive.[citation needed]

Tonic immobility[edit]

Apparent death of a beetle

Tonic immobility (TI) is a behaviour in which some animals become apparently temporarily paralysed and unresponsive to external stimuli. In most cases, this occurs in response to an extreme threat such as being captured by a (perceived) predator, although in sharks exhibiting the behaviour, some scientists relate it to mating.[citation needed]

In sharks[edit]

Some sharks can be induced into TI[2] by inverting them, e.g. lemon sharks and reef sharks.[citation needed] This state persists for an average of 15 minutes before recovery and the resumption of active behaviour. Scientists have exploited this response to study shark behaviour; chemical shark repellent have been studied to test the effectiveness and to more accurately estimate dose sizes, concentrations and time to recovery.[3] For tiger sharks (measuring 3–4 metres in length), TI can be induced by humans placing their hands lightly on the sides of the animal's snout in the area surrounding the eyes. Great White sharks have been shown to be less responsive than other species to the induction of tonic immobility. Scientists believe that tonic immobility displayed by sharks may be linked with mating, because female sharks seem more responsive than males.[4] During tonic immobility in sharks, the dorsal fin(s) straighten, and both breathing and muscle contractions become more steady and relaxed.

In marine mammals[edit]

In 1997, it was reported that around the Farallon Islands off the coast of California, a female orca was seen apparently inducing TI in a great white shark. The orca held the shark upside down to induce TI and kept the shark still for 15 minutes, causing it to suffocate to death. This was the first recorded case of predation on a great white shark in the wild by a species other than humans. Another case of orcas apparently inducing TI has been observed with stingrays in New Zealand. In this context, the orcas turn themselves upside down before attacking, trap the stingrays in their mouths then quickly right themselves. This inverts the stingray thereby inducing TI, rendering the fish helpless and an easy meal.[5]

In reptiles[edit]

Tonic immobility can be reliably induced in the lizard Iguana iguana by a combination of inversion, restraint and moderate pressure. During TI, there are obvious changes in respiration including a decline in respiration rate, the rhythm becomes sporadic, and the magnitude irregular. The prolonged period of TI does not seem to be consistent with the fear hypothesis, but could be the result of a period of cortical depression due to increased brain stem activity. [6]

Tonic immobility can also be induced in Anolis carolinensis. The characteristics of this TI vary as a function of the duration and condition of captivity.[7]

In rabbits[edit]

In rabbits, the physiological and behavioral responses to induced tonic immobility have been found to be indicative of a fear-motivated stress state, confirming that the promotion of TI to increase a bond between rabbits and their owners—thinking the rabbits enjoy it—is misplaced; however, some researchers conclude that inducing TI in rabbits is appropriate for certain procedures as it holds less risk than anesthesia.[8]

In humans[edit]

Tonic immobility has also been hypothesized to occur in humans who are subject to intense trauma such as sexual assault.[9][10]

As a scientific tool[edit]

Tonic immobility is considered to be a fear-potentiated response induced by physical restraint and characterised by reduced responsiveness to external stimulation. It has been used as a measure in the assessment of animal welfare, particularly hens, since 1970.[11][12][13] The rationale for the TI test is that the experimenter simulates a predator thereby eliciting the anti-predator response. The precept is that the prey animal 'pretends' to be dead to be able to escape when/if the predator relaxes its concentration. Death feigning birds often take advantage of escape opportunities; TI in quail reduces the probability of the birds being predated by cats.[14]

To induce tonic immobility, the animal is gently restrained on its side or back for a period of time, e.g. 15 seconds. This is done either on a firm, flat surface or sometimes in a purpose-built ‘V’ or ‘U’-shaped restraining cradle. In rodents, the response is sometimes induced by additionally pinching or attaching a clamp to the skin at the nape of the neck.[15] Scientists record behaviours such as the number of inductions (15 second restraining periods) required for the animal to remain still, the latency to the first major movements (often cycling motions of the legs), latency to first head or eye movements and the duration of immobility, sometimes called the ‘righting time’.

Tonic immobility has been used to show that hens in cages are more fearful than those in pens,[13] hens on the top tier of tiered battery cages are more fearful than those on the lower levels,[16] hens carried by hand are more fearful than hens carried on a mechanical conveyor,[17] and hens undergoing longer transportation times are more fearful than those undergoing transport of a shorter duration.[18]

Tonic immobility as a scientific tool has also been used with mice,[19] gerbils,[20] guinea pigs,[21] rats,[15] rabbits[22] and pigs.[23]


A grass snake playing dead

In animal behaviour, thanatosis (from the Greek noun θανάτωσις meaning "putting to death") is the process by which an animal feigns death in order to evade unwelcome attention. It can be for various reasons, such as that of a prey evading a predator, a male trying to mate with a female, or a predator trying to lure potential prey closer. The French biologist Georges Pasteur classifies it as a form of self-mimesis, a form of camouflage or mimicry in which the "mimic" imitates itself in a dead state.[24]

For defense[edit]

For defensive purposes, thanatosis hinges on the pursuers' becoming unresponsive to its victim, as most predators only catch live prey.[24]

In beetles, artificial selection experiments have shown that there is heritable variation for length of death-feigning. Those selected for longer death-feigning durations are at a selective advantage to those at shorter durations when a predator is introduced,[25] which suggests that thanatosis is indeed adaptive.

In the hog-nosed snake, a threatened individual rolls onto its back and appears to be dead when threatened by a predator, while a foul-smelling, volatile fluid oozes from its body. Predators, such as cats, then lose interest in the snake, which both looks, and smells, dead. One reason for their loss of interest is that rotten smelling animals are avoided as a precaution against infectious disease, so the snake is, in this case, exploiting that reaction. Newly hatched young also instinctively show this behaviour when rats try to eat them.[26]

In mammals, the Virginia opossum is perhaps the best known example of defensive thanatosis. "Playing possum" is an idiomatic phrase which means "pretending to be dead".[27] It comes from a characteristic of the Virginia opossum, which is famous for pretending to be dead when threatened.[28][29] This instinct does not always pay off in the modern world; for example, opossums scavenging roadkill may use it in response to the threat posed by oncoming traffic, and subsequently end up as roadkill themselves.[30]

"Playing possum" can also mean simply pretending to be injured, unconscious, asleep, or otherwise vulnerable, often to lure an opponent into a vulnerable position him or herself.[27]

Thanatosis has also been observed in some invertebrates such as the wasp, Nasonia vitripennis,[31] and the cricket, Gryllus bimaculatus.[32]

For reproduction[edit]

In the spider species Pisaura mirabilis, male spiders often stage elaborate rituals of gift-giving and thanatosis to avoid getting eaten by female spiders during mating. Studies have shown higher chances of success in mating with females for males who exhibit death-feigning more frequently than for males who do it less.[33]

For predation[edit]

Adult male Livingston's Cichlid (N. livingstonii)

Nimbochromis is a small genus of haplochromine cichlids mostly endemic to Lake Malawi in East Africa. They are known as 'sleeper cichlids' or (in Chichewa) kaligono ("sleepers"), due to their unique hunting behavior. In these large predatory fish, thanatosis is expressed as a form of aggressive mimicry. This fish will lie down on its side on the bottom sediments and assume a blotchy coloration. Scavengers, attracted to what seems like a dead fish, will approach the predator to investigate. N. livingstoni then abandons the pretense, righting itself again and quickly eating any scavenger unfortunate enough to come too close.[34]

See also[edit]


  1. ^ Gilman, T.T., Marcuse, F.L. and Moore, A.U., (1960). Animal hypnosis: a study of the induction of tonic immobility in chickens. Journal of Comparative Physiology and Psychology, 43: 99-111
  2. ^ Henningsen, A.D., (1994). Tonic immobility in 12 elasmobranchs - use as an aid in captive husbandry. Zoo Biology, 13: 325-332 doi:10.1002/zoo.1430130406
  3. ^ "Tonic immobility". Shark defense: Chemical repellents. Retrieved January 28, 2006. 
  4. ^ Sharkman - TV programme on Discovery Channel[dead link]
  5. ^ National Geographic Channel "The Whale That Ate Jaws" 11/29/2009
  6. ^ Prestrude, A.M. and Crawford, F.T. (1970). "Tonic immobility in the lizard, iguana iguana.". Animal Behaviour 18 (2): 391–395. 
  7. ^ Hennig, C.W and Dunlap, W.P. (1978). "Tonic immobility in Anolis carolinensis: Effects of time and conditions of captivity". Behavioral Biology 23 (1): 75–86. 
  8. ^ McBride, Anne et al. (2006). "Trancing rabbits: Relaxed hypnosis or a state of fear?". Proceedings of the VDWE International Congress on Companion Animal Behaviour and Welfare (VDWE International Congress on Companion Animal Behaviour and Welfare): pp. 135–137. Retrieved September 2, 2013.  (downloadable .doc file). • Click here for PDF copy from
  9. ^
  10. ^ "Talking about Tonic Immobility on Tonight’s SVU". Joyful Heart Foundation. 2012-10-10. Retrieved 2013-09-19. 
  11. ^ Gallup, G.G., Jr., Nash, R.F., Potter, R.J. and Donegan, N.H., (1970). Effect of varying conditions of fear on immobility reactions in domestic chickens (Gallus gullus). Journal of Comparative and Physiological Psychology, 73: 442-445
  12. ^ Gallup, G.G., Jr., (1979). Tonic immobility as a measure of fear in the domestic fowl. Animal Behaviour, 27: 316-317
  13. ^ a b Jones, B. and Faure, J.M. (1981). Tonic immobility ("righting time") in laying hens housed in cages and pens. Applied Animal Ethology 7: 369-372
  14. ^ Forkman, B., Boissy, A. Meunier-Salaün, M.-C. Canali, E. and Jones, R.B., (2007). A critical review of fear tests used on cattle, pigs, sheep, poultry and horses. Physiology & Behavior, 92: 340-374
  15. ^ a b Zamudio, S.R., Quevedo-Corona, L., Garcés, L. and De La Cruz, F. (2009). The effects of acute stress and acute corticosterone administration on the immobility response in rats. Brain Research Bulletin, 80: 331-336
  16. ^ Jones, R.B., (1987). Fearfulness of caged laying hens: The effects of cage level and type of roofing. Applied Animal Behaviour Science, 17: 171-175
  17. ^ Scott, G.B. and Moran, P., (1993). Fear levels in laying hens carried by hand and by mechanical conveyors. Applied Animal Behaviour Science, 36: 337-345
  18. ^ Cashman P. , Nicol, C.J. and Jones, R.B. (1989). Effects of transportation on the tonic immobility fear reactions of broilers. British Poultry Science, 30: 211-221
  19. ^ Bazovkina D.V., Tibeikina M.A., Kulikov A.V. and Popova, N.K., (2011). Effects of lipopolysaccharide and interleukin-6 on cataleptic immobility and locomotor activity in mice. Neuroscience Letters, 487: 302-304 doi:10.1016/j.neulet.2010.10.043
  20. ^ Griebel G., Stemmelin, J. and Scatton, B. (2005). Effects of the cannabinoid CB1 receptor antagonist rimonabant in models of emotional reactivity in rodents. Biological Psychiatry, 57: 261-267 doi:10.1016/j.biopsych.2004.10.032
  21. ^ Donatti A.F. and Leite-Panissi C.R.A. (2011). Activation of corticotropin-releasing factor receptors from the basolateral or central amygdala increases the tonic immobility response in guinea pigs: An innate fear behaviour. Behavioural Brain Research, 225: 23-30
  22. ^ Verwer, C.M., van Amerongen, G., van den Bos R. and Coenraad, F.M.H., (2009). Handling effects on body weight and behaviour of group-housed male rabbits in a laboratory setting. Applied Animal Behaviour Science, 117: 93-102 doi:10.1016/j.applanim.2008.12.004
  23. ^ Hessing, M.J.C., Hagelsø, A.M., Schouten, W.G.P., Wiepkema P.R. and van Beek, J.A.M. (1994). Individual behavioral and physiological strategies in pigs. Physiology and Behavior, 55: 39–46
  24. ^ a b Pasteur, G. (1982). "A classificatory review of mimicry systems". Annual Review of Ecology and Systematics 13: 169–199.
  25. ^ Miyatake, T; Katayama, K.; Takeda, Y.; Nakashima, A.; Mizumoto, M.; Mizumoto, M (2004). "Is death-feigning adaptive? Heritable variation in fitness difference of death-feigning behaviour". Proceedings of the Royal Society B 271 (1554): 2293–2296. doi:10.1098/rspb.2004.2858. PMC 1691851. PMID 15539355. 
  26. ^ Triumph of Life (2006). Alexandria, VA: PBS Home Video.
  27. ^ a b The Chambers Dictionary. Allied Publishers. 1998. p. 1279. ISBN 978-81-86062-25-8. 
  28. ^ Francq, E. (1969). "Behavioural aspects of feigned death in the opossum Didelphis marsupialis". American Midwest Naturalist (The University of Notre Dame) 81 (2): 556–568. doi:10.2307/2423988. JSTOR 2423988. 
  29. ^ Ann Bailey Dunn. "Playing Possum". Wonderful West Virginia. Retrieved May 11, 2011. 
  30. ^ "Virginia Opossum". Mass Audubon. Retrieved May 11, 2011. "Opossums are frequently encountered as corpses along highways. Some biologists believe that many die as they feed on road-killed animals – a favorite food. Others believe that the opossums’ small brain (5 times smaller than that of a raccoon) suggests that they may just be too dumb to get out of the way of vehicles!" 
  31. ^ King, B.; H. Leaich (2006). "Variation in propensity to exhibit thanatosis in Nasonia vitripennis (Hymenoptera: Pteromalidae)". Journal of Insect Behaviour 19 (2): 241–249. doi:10.1007/s10905-006-9022-7. 
  32. ^ Nishino, H. (2004). "Motor output characterizing thanatosis in the cricket Gryllus bimaculatus". Journal of Experimental Behaviour 207: 3899–3915. 
  33. ^ Line Spinner Hansen, Sofia Fernandez Gonzales, Søren Toft, & Trine Bilde (2008). "Thanatosis as an adaptive male mating strategy in the nuptial gift–giving spider Pisaura mirabilis". Behavioral Ecology 19 (3): 546–551. doi:10.1093/beheco/arm165. Retrieved May 11, 2011. 
  34. ^ Gene S. Helfman, Bruce B. Collette, & Douglas E. Facey (1997). The diversity of fishes. Wiley-Blackwell. p. 324. ISBN 978-0-86542-256-8. 

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