Apparent death

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

Apparent death, colloquially known as playing dead, feigning death, 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 Athanasius Kircher.


The term "thanatopsis" (Greek: thanatos "death" + opsis "a sight, view") may be more correct than "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]

Black house ants attacking a green-head ant which has gone into tonic immobility

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, arguing that biting by the male immobilizes the female and thus facilitates mating.[2]

In sharks[edit]

Some sharks can be induced into tonic immobility by inverting them and restraining them by hand, e.g. dogfish sharks, lemon sharks and reef sharks[disambiguation needed].[2][3][4][5] For tiger sharks (measuring 3–4 metres in length), tonic immobility can be induced by humans placing their hands lightly on the sides of the animal's snout in the area surrounding the eyes. During tonic immobility in sharks, the dorsal fins straighten, and both breathing and muscle contractions become more steady and relaxed. 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 their effectiveness and to more accurately estimate dose sizes, concentrations and time to recovery.[6] Tonic immobility can also be used as a form of mild anesthesia during experimental manipulations of sharks.[7][8]

Scientists also believe that tonic immobility can be a stressful experience for sharks. By measuring blood chemistry samples when the shark is immobile, it has been suggested that tonic immobility can actually put stress on the shark, and reduce breathing efficiency. However, it has also been proposed that sharks have a series of compensatory mechanisms that work to increase respiration rates and lower stress.[9]

In teleost fishes[edit]

Goldfish, trout, rudd, tench, brown bullhead, medaka, paradise fish, and topminnow have been reported to go limp when they are restrained on their backs.[10] Oscars seem to go into shock when they are stressed (when their aquarium is being cleaned, for example): they lie on their side, stop moving their fins, start to breathe more slowly and deeply, and lose colour.[11] A similar behavior has been reported for convict tangs in the field.[12]

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.[citation needed] 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.[13][full citation needed]

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.[14]

Tonic immobility can also be induced in the Carolina anole. The characteristics of this TI vary as a function of the duration and condition of captivity.[15]

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. Tonic immobility is considered a last attempt for prey to escape being eaten by a predator. In a study conducted by McBride et al. (McBride - Trancing Rabbits - Tonic Immobility) the results suggested that rabbits show symptoms that are in line with being stressed after being in a tonic immobility state, such as a faster heart rate and breathing. This confirms that the promotion of tonic immobility to increase a bond between rabbits and their owners — holding the rabbit on its back and thinking the rabbits enjoy it — is misplaced; however, some researchers conclude that inducing tonic immobility in rabbits is appropriate for certain veterinary procedures as it holds less risk than anesthesia.[16]

In humans[edit]

Tonic immobility has also been hypothesized to occur in humans who are subject to intense trauma such as sexual assault.[17][18]

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.[19][20][21] 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.[22]


Tonic immobility has been used to show that hens in cages are more fearful than those in pens,[21] hens on the top tier of tiered battery cages are more fearful than those on the lower levels,[24] hens carried by hand are more fearful than hens carried on a mechanical conveyor,[25] and hens undergoing longer transportation times are more fearful than those undergoing transport of a shorter duration.[26]

Tonic immobility as a scientific tool has also been used with mice,[27] gerbils,[28] guinea pigs,[29] rats,[23] rabbits[30] and pigs.[31]


Eastern hog-nosed snake playing dead and regurgitating some toad
Brown widow spider resorting to thanatosis after being shaken from her web
Cichlids of the genus Nimbochromis express thanatosis as a form of aggressive mimicry, playing dead to attract prey


For defense[edit]


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,[33] 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.[34]

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".[35] It comes from a characteristic of the Virginia opossum, which is famous for pretending to be dead when threatened.[36][37] 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.[38]


Thanatosis has also been observed in some invertebrates such as the wasp, Nasonia vitripennis,[39] and the cricket, Gryllus bimaculatus.[40]

For reproduction[edit]


For predation[edit]

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.[42][43] A similar strategy has also been observed in the African cichlid Lamprologus lemairii from Lake Tanganyika [44] and in the Central American yellowjacket cichlid Parachromis friedrichsthalii.[45]

See also[edit]


  2. ^ a b 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. ^ Whitman, P.A., Marshall, J.A., and Keller, E.C.Jr. (1986) Tonic immobility in the smooth dogfish shark, Mustelus canis (Pisces, Carcharhinidae). Copeia 1986: 829-832.
  4. ^ Watsky, M.A., and Gruber, S.H. (1990) Induction and duration of tonic immobility in the lemon shark, Negaprion brevirostris. Fish Physiology and Biochemistry 8: 207-210.
  5. ^ Davie, P.S., Franklin, C.E., and Grigg, G.C. (1993) Blood pressure and heart rate during tonic immobility in the black tipped reef shark, Carcharhinus melanoptera. Fish Physiology and Biochemistry 12: 95-100.
  6. ^ "Tonic immobility". Shark defense: Chemical repellents. Retrieved January 28, 2006. 
  7. ^ Heithaus, M.R., Dill, L.M., Marshall, G.J., and Buhleier, B. (2002) Habitat use and foraging behavior of tiger sharks (Galeocerdo cuvier) in a seagrass ecosystem. Marine Biology 140: 237-248.
  8. ^ Holland, K.N., Wetherbee, B.M., owe, C.G., and Meyer, C.G. (1999) Movements of tiger sharks (Galeocerdo cuvier) in coastal Hawaiian waters. Marine Biology 134: 665-673.
  9. ^ Brooks, E. J., et al. "The Stress Physiology of Extended Duration Tonic Immobility in the Juvenile Lemon Shark, Negaprion Brevirostris (Poey 1868)." Journal of experimental marine biology and ecology 409.1-2 (2011): 351-60. SCOPUS. Web. 22 Apr. 2015.
  11. ^ Crawford, F.T. (1977) Induction and duration of tonic immobility. The Psychological Record 27: 89-107.
  12. ^ Howe, J.C. (1991) Field observations of death feigning in the convict tang, Acanthurus triostegus (Linnaeus), with comments on the nocturnal color pattern in juvenile specimens. Journal of Aquariculture and Aquatic Sciences 6: 13-15.
  13. ^ National Geographic Channel "The Whale That Ate Jaws" 11/29/2009
  14. ^ Prestrude, A.M. and Crawford, F.T. (1970). "Tonic immobility in the lizard, iguana iguana.". Animal Behaviour 18 (2): 391–395. doi:10.1016/s0003-3472(70)80052-5. 
  15. ^ 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. doi:10.1016/s0091-6773(78)91180-x. 
  16. ^ 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
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  18. ^ "Talking about Tonic Immobility on Tonight’s SVU". Joyful Heart Foundation. 2012-10-10. Retrieved 2013-09-19. 
  26. ^ 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
  27. ^ 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
  28. ^ 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
  32. ^ a b Pasteur, G. (1982). "A classificatory review of mimicry systems". Annual Review of Ecology and Systematics 13: 169–199.
  33. ^ 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. 
  34. ^ Triumph of Life (2006). Alexandria, VA: PBS Home Video.
  35. ^ a b The Chambers Dictionary. Allied Publishers. 1998. p. 1279. ISBN 978-81-86062-25-8. 
  36. ^ 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. 
  37. ^ Ann Bailey Dunn. "Playing Possum". Wonderful West Virginia. Retrieved May 11, 2011. 
  38. ^ "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! 
  39. ^ 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. 
  40. ^ Nishino, H. (2004). "Motor output characterizing thanatosis in the cricket Gryllus bimaculatus". Journal of Experimental Behaviour 207: 3899–3915. doi:10.1242/jeb.01220. 
  41. ^ 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. 
  42. ^ Gene S. Helfman, Bruce B. Collette, & Douglas E. Facey (1997). The diversity of fishes. Wiley-Blackwell. p. 324. ISBN 978-0-86542-256-8. 
  43. ^ McKaye, K.R. (1981) Field observation on death feigning: a unique hunting behavior by the predatory cichlid, Haplochromis livingstonii, of Lake Malawi. Environmental Biology of Fishes 6: 361-365.
  44. ^ Lucanus, O. (1998) Darwin’s pond: Malawi and Tanganyika. Tropical Fish Hobbyist 47: 150-154.
  45. ^ Tobler, M. (2005) Feigning death in the Central American cichlid Parachromis friedrichsthalii. Journal of Fish Biology 66: 877-881.

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