Snakes have been important ambush predators of both primates and human hunter-gatherers throughout their co-evolutionary history. Viperid snakes in particular are responsible for most fatal venomous snakebites worldwide and thus represent a strong selective pressure. They elicit intense fear in humans and are easily recognizable thanks to their distinctive morphotype. In this study, we measured skin resistance (SR) and heart rate (HR) in human subjects exposed to snake pictures eliciting either high fear (10 venomous viperid species) or disgust (10 nonvenomous fossorial species). Venomous snakes subjectively evaluated as frightening trigger a stronger physiological response (higher SR amplitude) than repulsive non-venomous snakes. However, stimuli presented in a block (more intense stimulation) do not trigger a stronger emotional response compared to sequentially presented stimuli (less intense stimulation). There are significant interindividual differences as subjects with high fear of snakes confronted with images of viperid snakes show stronger, longer-lasting, and more frequent changes in SR and higher HR compared to low-fear subjects. Thus, we show that humans demonstrate a remarkable ability to discriminate between dangerous viperids and harmless fossorial snakes, which is also reflected in distinct autonomous body responses.

Department of Psychology Faculty of Arts Charles University Prague Czech Republic

Department of Zoology Faculty of Science Charles University Prague Czech Republic

National Institute of Mental Health Klecany Czech Republic

Zobrazit více v PubMed

Isbell LA. Snakes as agents of evolutionary change in primate brains. J Hum Evol. 2006;51(1):1–35. 10.1016/j.jhevol.2005.12.012 PubMed DOI

Öhman A, Flykt A, Esteves F. Emotion drives attention: Detecting the snake in the grass. J Exp Psychol Gen. 2001;130(3):466–478. 10.1037//0096-3445.130.3.466 PubMed DOI

Shibasaki M, Kawai N. Rapid Detection of Snakes by Japanese Monkeys (Macaca fuscata): An Evolutionarily Predisposed Visual System. J Comp Psychol. 2009;123(2):131–135. 10.1037/a0015095 PubMed DOI

Lobue V, Rakison DH. What we fear most: A developmental advantage for threat-relevant stimuli. Dev Rev. 2013;33(4):285–303.

McGrew WC. Snakes as hazards: modelling risk by chasing chimpanzees. Primates. 2015;56(2):107–111. 10.1007/s10329-015-0456-4 PubMed DOI

Headland TN, Greene HW. Hunter-gatherers and other primates as prey, predators, and competitors of snakes. P Natl Acad Sci USA. 2011;108(52):E1470–E1474. PubMed PMC

Uetz P, Freed P, Hošek J. The Reptile Database [accessed 2019]. Available from: http://www.reptile-database.org/.

Fry BG, Vidal N, Norman JA, Vonk FJ, Scheib H, Ramjan SFR, et al. Early evolution of the venom system in lizards and snakes. Nature. 2006;439(7076):584–588. 10.1038/nature04328 PubMed DOI

World Health Organization. Snakebite envenoming 2019. Available from: http://www.who.int/news-room/fact-sheets/detail/snakebite-envenoming.

Fry BG. Snakebite: When the Human Touch Becomes a Bad Touch. Toxins. 2018;10(4). PubMed PMC

Swaroop S, Grab B. Snakebite mortality in the world. B World Health Organ. 1954;10(1):35–76. PubMed PMC

Chippaux JP. Snake-bites: appraisal of the global situation. B World Health Organ. 1998;76(5):515–524. PubMed PMC

Valenta J. Jedovatí hadi: intoxikace, terapie. Prague, Czech Republic: Galén; 2008.

Sutherland SK. Deaths from Snake Bite in Australia, 1981–1991. Med J Australia. 1992;157(11–12):740–746. PubMed

Rádlová S, Janovcová M, Sedláčková K, Polák J, Nácar D, Peléšková Š, et al. Snakes Represent Emotionally Salient Stimuli That May Evoke Both Fear and Disgust. Front Psychol. 2019;10(1085). PubMed PMC

Öhman A, Mineka S. Fears, phobias, and preparedness: Toward an evolved module of fear and fear learning. Psychol Rev. 2001;108(3):483–522. 10.1037/0033-295x.108.3.483 PubMed DOI

Öhman A. The role of the amygdala in human fear: Automatic detection of threat. Psychoneuroendocrino. 2005;30(10):953–958. PubMed

Öhman A, Carlsson K, Lundqvist D, Ingvar M. On the unconscious subcortical origin of human fear. Physiol Behav. 2007;92(1–2):180–185. 10.1016/j.physbeh.2007.05.057 PubMed DOI

Rosen JB, Donley MP. Animal studies of amygdala function in fear and uncertainty: Relevance to human research. Biol Psychol 2006;73(1):49–60. 10.1016/j.biopsycho.2006.01.007 PubMed DOI

DeLoache JS, LoBue V. The narrow fellow in the grass: human infants associate snakes and fear. Developmental Sci. 2009;12(1):201–207. PubMed

Mcnally RJ. Preparedness and Phobias—a Review. Psychol Bull. 1987;101(2):283–303. PubMed

Öhman A, Dimberg U, Esteves F. Preattentive activation of aversive emotions In: Archer T, Nilsson LG, editors. Aversion, avoidance and anxiety. New York, USA: Psychology Press; 2014. p. 169–193.

Öhman A, Soares JJF. On the Automatic Nature of Phobic Fear: Conditioned Electrodermal Responses to Masked Fear-Relevant Stimuli. J Abnorm Psychol. 1993;102(1):121–132. 10.1037//0021-843x.102.1.121 PubMed DOI

Öhman A, Soares JJF. "Unconscious Anxiety": Phobic Responses to Masked Stimuli. J Abnorm Psychol. 1994;103(2):231–240. 10.1037//0021-843x.103.2.231 PubMed DOI

Öhman A, Soares JJF. Emotional conditioning to masked stimuli: Expectancies for aversive outcomes following nonrecognized fear-relevant stimuli. J Exp Psychol Gen. 1998;127(1):69–82. 10.1037//0096-3445.127.1.69 PubMed DOI

Grassini S, Holm SK, Railo H, Koivisto M. Who is afraid of the invisible snake? Subjective visual awareness modulates posterior brain activity for evolutionarily threatening stimuli. Biol Psychol. 2016;121:53–61. 10.1016/j.biopsycho.2016.10.007 PubMed DOI

Öhman A, Mineka S. The malicious serpent: Snakes as a prototypical stimulus for an evolved module of fear. Curr Dir Psychol Sci. 2003;12(1):5–9.

Landová E, Bakhshaliyeva N, Janovcová M, Peléšková Š, Suleymanova M, Polák J, et al. Association Between Fear and Beauty Evaluation of Snakes: Cross-Cultural Findings. Front Psychol. 2018;9 10.3389/fpsyg.2018.00009 PubMed DOI PMC

Klieger DM, Siejak KK. Disgust as the source of false positive effects in the measurement of ophidiophobia. J Psychol. 1997;131(4):371–382. 10.1080/00223989709603523 PubMed DOI

Janovcová M, Rádlová S, Polák J, Sedláčková K, Peléšková Š, Žampachová B, et al. Human Attitude toward Reptiles: A Relationship between Fear, Disgust, and Aesthetic Preferences. Animals-Basel. 2019;9(5):238–254. PubMed PMC

Ekman P. An Argument for Basic Emotions. Cognition Emotion. 1992;6(3–4):169–200.

Davidson RJ, Saron CD, Senulis JA, Ekman P, Friesen WV. Approach Withdrawal and Cerebral Asymmetry—Emotional Expression and Brain Physiology .1. J Pers Soc Psychol. 1990;58(2):330–341. PubMed

Woody SR, Teachman BA. Intersection of disgust and fear: Normative and pathological views. Clin Psychol-Sci Pr. 2000;7(3):291–311.

Cisler JM, Olatunji BO, Lohr JM. Disgust, fear, and the anxiety disorders: A critical review. Clin Psychol Rev. 2009;29(1):34–46. 10.1016/j.cpr.2008.09.007 PubMed DOI PMC

LeDoux J. Rethinking the Emotional Brain. Neuron. 2012;73(4):653–676. 10.1016/j.neuron.2012.02.004 PubMed DOI PMC

Barrett LF, Lewis M, Haviland-Jones JM, editors. Handbook of Emotions. 4th ed New York, USA: Guilford Press; 2016.

Polák J, Rádlová S, Janovcová M, Flegr J, Landová E, Frynta D. Scary and nasty beasts: Self‐reported fear and disgust of common phobic animals. Brit J Psychol. 2019; first online. PubMed

Davey GCL, Marzillier S. Disgust and animal phobias In: Olatunji BO, McKay D, editors. Disgust and its disorders: theory, assessment, and treatment implications. Washington, DC, USA: American Psychological Association; 2009. p. 169–190.

Rozin P, Haidt J, Fincher K. From Oral to Moral. Science. 2009;323(5918):1179–1180. 10.1126/science.1170492 PubMed DOI

Oaten M, Stevenson RJ, Case TI. Disgust as a Disease-Avoidance Mechanism. Psychol Bull. 2009;135(2):303–321. 10.1037/a0014823 PubMed DOI

Curtis V, de Barra M, Aunger R. Disgust as an adaptive system for disease avoidance behaviour. Philos T R Soc B. 2011;366(1563):389–401. PubMed PMC

Schaller M, Park JH. The Behavioral Immune System (and Why It Matters). Curr Dir Psychol Sci. 2011;20(2):99–103.

Cacioppo JT, Berntson GG, Larsen JT, Poehlmann KM, Ito TA. The psychophysiology of emotion In: Lewis M, Haviland-Jones JM, editors. Handbook of emotions. 2nd ed New York, USA: Guilford Press; 2000. p. 173–191.

Kreibig SD. Autonomic nervous system activity in emotion: A review. Biol Psychol. 2010;84(3):394–421. 10.1016/j.biopsycho.2010.03.010 PubMed DOI

Ekman P, Levenson RW, Friesen WV. Autonomic Nervous-System Activity Distinguishes among Emotions. Science. 1983;221(4616):1208–1210. 10.1126/science.6612338 PubMed DOI

Palomba D, Sarlo M, Angrilli A, Mini A, Stegagno L. Cardiac responses associated with affective processing of unpleasant film stimuli. Int J Psychophysiol. 2000;36(1):45–57. 10.1016/s0167-8760(99)00099-9 PubMed DOI

Kreibig SD, Wilhelm FH, Roth WT, Gross JJ. Cardiovascular, electrodermal, and respiratory response patterns to fear- and sadness-inducing films. Psychophysiology. 2007;44(5):787–806. 10.1111/j.1469-8986.2007.00550.x PubMed DOI

Lang PJ, Greenwald MK, Bradley MM, Hamm AO. Looking at Pictures: Affective, Facial, Visceral, and Behavioral Reactions. Psychophysiology. 1993;30(3):261–273. 10.1111/j.1469-8986.1993.tb03352.x PubMed DOI

Russell JA. Core affect and the psychological construction of emotion. Psychol Rev. 2003;110(1):145–172. 10.1037/0033-295x.110.1.145 PubMed DOI

Barrett LF. Solving the emotion paradox: Categorization and the experience of emotion. Pers Soc Psychol Rev. 2006;10(1):20–46. 10.1207/s15327957pspr1001_2 PubMed DOI

Coelho CM, Suttiwan P, Faiz A, Ferreira-Santos F, Zsido AN. Are Humans Prepared to Detect, Fear, and Avoid Snakes? The Mismatch Between Laboratory and Ecological Evidence. Front Psychol. 2019;10(2094). PubMed PMC

Öhman A, Fredrikson M, Hugdahl K, Rimmö PA. The premise of equipotentiality in human classical conditioning: conditioned electrodermal responses to potentially phobic stimuli. J Exp Psychol Gen. 1976;105(4):313–337. 10.1037//0096-3445.105.4.313 PubMed DOI

Fredrikson M, Öhman A. Cardiovascular and Electrodermal Responses Conditioned to Fear-Relevant Stimuli. Psychophysiology. 1979;16(1):1–7. 10.1111/j.1469-8986.1979.tb01428.x PubMed DOI

Soares JJF, Öhman A. Backward Masking and Skin Conductance Responses after Conditioning to Nonfeared but Fear-Relevant Stimuli in Fearful Subjects. Psychophysiology. 1993;30(5):460–466. 10.1111/j.1469-8986.1993.tb02069.x PubMed DOI

Soares JJF, Öhman A. Preattentive Processing, Preparedness and Phobias—Effects of Instruction on Conditioned Electrodermal Responses to Masked and Nonmasked Fear-Relevant Stimuli. Behav Res Ther. 1993;31(1):87–95. 10.1016/0005-7967(93)90046-w PubMed DOI

Dimberg U, Hansson G, Thunberg M. Fear of snakes and facial reactions: A case of rapid emotional responding. Scand J Psychol. 1998;39(2):75–80. PubMed

Rachman S. The conditioning theory of fear acquisition: A critical examination. Behav Res Ther. 1977;15(5):375–387. 10.1016/0005-7967(77)90041-9 PubMed DOI

Smith SM. Coral-Snake Pattern-Recognition and Stimulus Generalization by Naive Great Kiskadees (Aves: Tyrannidae). Nature. 1977;265(5594):535–536.

Landová E, Musilová V, Polák J, Sedláčková K, Frynta D. Antipredatory reaction of the leopard gecko Eublepharis macularius to snake predators. Curr Zool. 2016;62(5):439–450. 10.1093/cz/zow050 PubMed DOI PMC

King GE. The attentional basis for primate responses to snakes. Annual meeting of the American Society of Primatologists; San Diego, CA, 1997.

Weiss L, Brandl P, Frynta D. Fear reactions to snakes in naive mouse lemurs and pig-tailed macaques. Primates. 2015;56(3):279–284. 10.1007/s10329-015-0473-3 PubMed DOI

Rádlová S, Polák J, Janovcová M, Sedláčková K, Peléšková Š, Landová E, et al. Emotional Reaction to Fear-and Disgust-Evoking Snakes: Sensitivity and Propensity in Snake-Fearful Respondents. Front Psychol. 2020;11(31). PubMed PMC

Klorman R, Weerts TC, Hastings JE, Melamed BG, Lang PJ. Psychometric description of some specific-fear questionnaires. Behav Ther. 1974;5(3):401–409.

Polák J, Sedláčková K, Nácar D, Landová E, Frynta D. Fear the serpent: A psychometric study of snake phobia. Psychiat Res. 2016;242:163–168. PubMed

Haidt J, Mccauley C, Rozin P. Individual-Differences in Sensitivity to Disgust—a Scale Sampling 7 Domains of Disgust Elicitors. Pers Indiv Differ. 1994;16(5):701–713.

Olatunji BO, Williams NL, Tolin DF, Abramowitz JS, Sawchuk CN, Lohr JM, et al. The disgust scale: Item analysis, factor structure, and suggestions for refinement. Psychol Assessment. 2007;19(3):281–297. PubMed

Polák J, Landová E, Frynta D. Undisguised disgust: a psychometric evaluation of a disgust propensity measure. Curr Psychol. 2019;38(3):608–617.

Nock MK, Wedig MM, Holmberg EB, Hooley JM. The emotion reactivity scale: Development, evaluation, and relation to self-injurious thoughts and behaviors. Behav Ther. 2008;39(2):107–116. 10.1016/j.beth.2007.05.005 PubMed DOI

Faul F, Erdfelder E, Lang A-G, Buchner A. G*Power 3: A flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Beh Res Methods. 2007;39,175–191. PubMed

Fredrikson M, Annas P, Fischer H, Wik G. Gender and age differences in the prevalence of specific fears and phobias. Behav Res Ther. 1996;34(1):33–39. 10.1016/0005-7967(95)00048-3 PubMed DOI

Snake Database [accessed 2019]. Available from: www.snakedatabase.org.

Spawls S, Howell K, Drewes R, Ashe J. A Field Guide to the Reptiles of East Africa. Princeton, NJ, USA: Princeton University Press; 2001.

Favreau P, Cheneval O, Menin L, Michalet S, Gaertner H, Principaud F, et al. The venom of the snake genus Atheris contains a new class of peptides with clusters of histidine and glycine residues. Rapid Commun Mass Sp. 2007;21(3):406–412. PubMed

Coborn J. The atlas of snakes of the world. Neptune City, NJ, USA: T.F.H. Publications; 1991.

Clinical Toxinology Resources [accessed 2019]. Available from: www.toxinology.com.

Chirio L, LeBreton M. Atlas des reptiles du Cameroun. Paris, France: Muséum National d'Histoire Naturelle; 2007.

Living Hazards Database [accessed 2019]. Available from: www.acq.osd.mil/eie/afpmb/docs/lhd/venomous_animals_byspecies.pdf.

Mirtschin PJ, Dunstan N, Hough B, Hamilton E, Klein S, Lucas J, et al. Venom yields from Australian and some other species of snakes. Ecotoxicology. 2006;15(6):531–538. 10.1007/s10646-006-0089-x PubMed DOI

Baha El Din S. A Guide to the Reptiles and Amphibians of Egypt. Cairo, Egypt: The American University in Cairo Press; 2006.

Behler JL, King FV. Field Guide to North American Reptiles and Amphibians. New York, NJ, USA: Alfred A. Knopf; 2002.

LD50 [accessed 2019]. Available from: www.seanthomas.net/oldsite/ld50tot.html.

Khan MS. A Guide to The Snakes of Pakistan. Frankfurt am Main, Germany: NHBS; 2002.

Das I. A Field Guide to the Reptiles of South-east Asia. London, United Kingdom: Bloomsbury Publishing; 2015.

Frynta D, Lišková S, Bultmann S, Burda H. Being Attractive Brings Advantages: The Case of Parrot Species in Captivity. Plos One. 2010;5(9):e12568 10.1371/journal.pone.0012568 PubMed DOI PMC

Lišková S, Frynta D. What Determines Bird Beauty in Human Eyes? Anthrozoos. 2013;26(1):27–41.

Frynta D, Peléšková Š, Rádlová S, Janovcová M, Landová E. Human evaluation of amphibian species: a comparison of disgust and beauty. Sci Nat. 2019;106(7–8):41. PubMed

Kašpar J, Hon Z, Janatová M, Smrčka P, Vítězník M, Hána K, et al., inventors. A biotelemetric system for the support of monitoring the psychophysiological state of a human being. Czech patent no. CZ306895B6; 2017. Retrieved from: https://isdv.upv.cz/webapp/resdb.print_detail.det?pspis=PT/2014-979&plang=EN

Pohlert T. The Pairwise Multiple Comparison of Mean Ranks Package (PMCMR). R package; 2014. Available from: https://CRAN.R-project.org/package=PMCMR.

Oksanen J, Blanchet FG, Friendly M, Kindt R, Legendre P, McGlinn D, et al. Vegan: Community Ecology Package. R Package Version 2.4–5; 2017. Available from: https://CRAN.R-project.org/package=vegan.

Stoffel MA, Nakagawa S, Schielzeth H. rptR: repeatability estimation and variance decomposition by generalized linear mixed-effects models. Methods Ecol Evol. 2017;8(11):1639–1644. Available from: https://CRAN.R-project.org/package=rptR.

Lessells CM, Boag PT. Unrepeatable Repeatabilities: a Common Mistake. Auk. 1987;104(1):116–121.

Nakagawa S, Schielzeth H. Repeatability for Gaussian and non‐Gaussian data: a practical guide for biologists. Biol Rev. 2010;85(4):935–956. 10.1111/j.1469-185X.2010.00141.x PubMed DOI

R Core Team. R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2017. Available from: https://www.R-project.org/.

TIBCO Software Inc. Statistica (data analysis software system), version 13; 2017. Available from: http://statistica.io.

Bradley MM, Cuthbert BN, Lang PJ. Picture media and emotion: Effects of a sustained affective context. Psychophysiology. 1996;33(6):662–670. 10.1111/j.1469-8986.1996.tb02362.x PubMed DOI

Murakami H, Matsunaga M, Ohira H. Phasic heart rate responses for anticipated threat situations. Int J Psychophysiol. 2010;77(1):21–25. 10.1016/j.ijpsycho.2010.03.012 PubMed DOI

Klorman R. Habituation of Fear: Effects of Intensity and Stimulus Order. Psychophysiology. 1974;11(1):15–26. 10.1111/j.1469-8986.1974.tb00817.x PubMed DOI

Wangelin BC, Low A, McTeague LM, Bradley MM, Lang PJ. Aversive picture processing: Effects of a concurrent task on sustained defensive system engagement. Psychophysiology. 2011;48(1):112–116. 10.1111/j.1469-8986.2010.01041.x PubMed DOI

Sanchez-Navarro JP, Martinez-Selva JM, Maldonado EF, Carrillo-Verdejo E, Pineda S, Torrente G. Autonomic reactivity in blood-injection-injury and snake phobia. J Psychosom Res. 2018;115:117–124. 10.1016/j.jpsychores.2018.10.018 PubMed DOI

Dilger S, Straube T, Mentzel HJ, Fitzek C, Reichenbach HR, Hecht H, et al. Brain activation to phobia-related pictures in spider phobic humans: an event-related functional magnetic resonance imaging study. Neurosci Lett. 2003;348(1):29–32. 10.1016/s0304-3940(03)00647-5 PubMed DOI

Goossens L, Sunaert S, Peeters R, Griez EJL, Schruers KRJ. Amygdala Hyperfunction in phobic fear normalizes after exposure. Biol Psychiat. 2007;62(10):1119–1125. 10.1016/j.biopsych.2007.04.024 PubMed DOI

Ahs F, Pissiota A, Michelgard A, Frans O, Furmark T, Appel L, et al. Disentangling the web of fear: Amygdala reactivity and functional connectivity in spider and snake phobia. Psychiat Res-Neuroim. 2009;172(2):103–108. PubMed

Courtney CG, Dawson ME, Schell AM, Parsons TD. Affective Computer-Generated Stimulus Exposure: Psychophysiological Support for Increased Elicitation of Negative Emotions in High and Low Fear Subjects In: Schmorrow DD, Estabrooke IV, Grootjen M, editors. Foundations of Augmented Cognition: Neuroergonomics and Operational Neuroscience; FAC 2009; Lecture Notes in Computer Science: Springer, Berlin, Heidelberg; 2009. p. 459–468.

Courtney CG, Dawson ME, Schell AM, Iyer A, Parsons TD. Better than the real thing: Eliciting fear with moving and static computer-generated stimuli. Int J Psychophysiol. 2010;78(2):107–114. 10.1016/j.ijpsycho.2010.06.028 PubMed DOI

Craske MG, Sipsas A. Animal Phobias Versus Claustrophobias—Exteroceptive Versus Interoceptive Cues. Behav Res Ther. 1992;30(6):569–581. 10.1016/0005-7967(92)90002-x PubMed DOI

Flykt A, Caldara R. Tracking fear in snake and spider fearful participants during visual search: A multi-response domain study. Cognition Emotion. 2006;20(8):1075–1091.

Flykt A, Banziger T, Lindeberg S. Intensity of vocal responses to spider and snake pictures in fearful individuals. Aust J Psychol. 2017;69(3):184–191.

May JR. Psychophysiology of Self-Regulated Phobic Thoughts. Behav Ther. 1977;8(2):150–159.

Schaefer HS, Larson CL, Davidson RJ, Coan JA. Brain, body, and cognition: Neural, physiological and self-report correlates of phobic and normative fear. Biol Psychol. 2014;98:59–69. 10.1016/j.biopsycho.2013.12.011 PubMed DOI PMC

Wikström J, Lundh LG, Westerlund J, Hogman L. Preattentive bias for snake words in snake phobia? Behav Res Ther. 2004;42(8):949–970. 10.1016/j.brat.2003.07.002 PubMed DOI

Nili U, Goldberg H, Weizman A, Dudai Y. Fear Thou Not: Activity of Frontal and Temporal Circuits in Moments of Real-Life Courage. Neuron. 2010;66(6):949–962. 10.1016/j.neuron.2010.06.009 PubMed DOI

Lueken U, Kruschwitz JD, Muehlhan M, Siegert J, Hoyer J, Wittchen HU. How specific is specific phobia? Different neural response patterns in two subtypes of specific phobia. Neuroimage. 2011;56(1):363–372. 10.1016/j.neuroimage.2011.02.015 PubMed DOI

Vrana SR. The psychophysiology of disgust: motivation, action, and autonomic support In: Olatunji BO, McKay D, editors. Disgust and Its Disorders: Theory, Assessment, and Treatment Implications. Washington, DC, USA: American Psychological Association; 2009. p. 123–143.

Redondo B, Vera J, Luque-Casado A, García-Ramos A, Jiménez R. Associations between accommodative dynamics, heart rate variability and behavioural performance during sustained attention: A test-retest study. Vision Res. 2019;163:24–32. 10.1016/j.visres.2019.07.001 PubMed DOI

Bell AM, Hankison SJ, Laskowski KL. The repeatability of behaviour: a meta-analysis. Anim Behav. 2009;77(4):771–783. 10.1016/j.anbehav.2008.12.022 PubMed DOI PMC

Hayes WK, Herbert SS, Rehling GC, Gennaro JF. Factors that influence venom expenditure in viperids and other snake species during predatory and defensive contexts In: Schuett GW, Höggren M, Douglas ME, Green HW, editors. Biology of the Vipers. Eagle Mountain, USA: Eagle Mountain Publishing; 2002. p. 207–233.

Marsh N, Gattullo D, Pagliaro P, Losano G. The gaboon viper, Bitis gabonica: Hemorrhagic, metabolic, cardiovascular and clinical effects of the venom. Life Sci. 1997;61(8):763–769. 10.1016/s0024-3205(97)00244-0 PubMed DOI

Mebs D, Ehrenfeld M, Samejima Y. Local Necrotizing Effect of Snake-Venoms on Skin and Muscle—Relationship to Serum Creatine-Kinase. Toxicon. 1983;21(3):393–404. 10.1016/0041-0101(83)90096-x PubMed DOI

Margres MJ, McGivern JJ, Wray KP, Seavy M, Calvin K, Rokyta DR. Linking the transcriptome and proteome to characterize the venom of the eastern diamondback rattlesnake (Crotalus adamanteus). J Proteomics. 2014;96:145–158. 10.1016/j.jprot.2013.11.001 PubMed DOI

Farid TM, Tu AT, Elasmar MF. Effect of Cerastobin, a Thrombinlike Enzyme from Cerastes-Vipera (Egyptian Sand Snake) Venom, on Human Platelets. Haemostasis. 1990;20(5):296–304. 10.1159/000216141 PubMed DOI

Hyde J, Ryan KM, Waters AM. Psychophysiological Markers of Fear and Anxiety. Curr Psychiat Rep. 2019;21(7):56. PubMed

Rohrmann S, Hopp H. Cardiovascular indicators of disgust. Int J Psychophysiol. 2008;68(3):201–208. 10.1016/j.ijpsycho.2008.01.011 PubMed DOI

de Jong PJ, van Overveld M, Peters ML. Sympathetic and parasympathetic responses to a core disgust video clip as a function of disgust propensity and disgust sensitivity. Biol Psychol. 2011;88(2–3):174–179. 10.1016/j.biopsycho.2011.07.009 PubMed DOI

Marsh N, Whaler B. The effects of snake venoms on the cardiovascular and haemostatic mechanisms. Int J Biochem. 1978;9(4):217–220. 10.1016/0020-711x(78)90001-0 PubMed DOI

Schaeffer RC, Briston C, Chilton SM, Carlson RW. Hypotensive and Hemostatic Properties of Rattlesnake (Crotalus-Viridis-Helleri) Venom and Venom Fractions in Dogs. J Pharmacol Exp Ther. 1984;230(2):393–398. PubMed

de Mesquita LCM, Selistre HS, Giglio JR. The Hypotensive Activity of Crotalus-Atrox (Western Diamondback Rattlesnake) Venom—Identification of Its Origin. Am J Trop Med Hyg. 1991;44(3):345–353. 10.4269/ajtmh.1991.44.345 PubMed DOI

Tibballs J. The cardiovascular, coagulation and haematological effects of Tiger Snake (Notechis scutatus) venom. Anaesth Intens Care. 1998;26(5):529–535. PubMed

Koh CY, Kini M. From snake venom toxins to therapeutics—Cardiovascular examples. Toxicon. 2012;59(4):497–506. 10.1016/j.toxicon.2011.03.017 PubMed DOI

Tunpe Ayeayemyint, Khineihan Thiha, Tinnuswe. Local Compression Pads as a First-Aid Measure for Victims of Bites by Russells Viper (Daboia-Russelii-Siamensis) in Myanmar. T Roy Soc Trop Med H. 1995;89(3):293–295. PubMed

Currie BJ, Canale E, Isbister GK. Effectiveness of pressure-immobilization first aid for snakebite requires further study. Emerg Med Australas. 2008;20(3):267–270. 10.1111/j.1742-6723.2008.01093.x PubMed DOI

Why Are Some Snakes More Terrifying and What Is Behind the Fear?

Hooding cobras can get ahead of other snakes in the ability to evoke human fear

Attentional, emotional, and behavioral response toward spiders, scorpions, crabs, and snakes provides no evidence for generalized fear between spiders and scorpions

Are vipers prototypic fear-evoking snakes? A cross-cultural comparison of Somalis and Czechs

The bigger the threat, the longer the gaze? A cross-cultural study of Somalis and Czechs

Animals evoking fear in the Cradle of Humankind: snakes, scorpions, and large carnivores

Human emotional evaluation of ancestral and modern threats: fear, disgust, and anger

The Ultimate List of the Most Frightening and Disgusting Animals: Negative Emotions Elicited by Animals in Central European Respondents