The evil eye effect: vertical pupils are perceived as more threatening

Popular culture has many examples of evil characters having vertically pupilled eyes. Humans have a long evolutionary history of rivalry with snakes and their visual systems were evolved to rapidly detect snakes and snake-related cues. Considering such evolutionary background, we hypothesised that humans would perceive vertical pupils, which are characteristics of ambush predators including some of the snakes, as threatening. In seven studies (aggregate N?=?1458) conducted on samples from American and Turkish samples, we found that vertical pupils are perceived as more threatening on both explicit (Study 1) and implicit level (Studies 2–7) and they are associated with physical, rather than social, threat (Study 4). Findings provided partial support regarding our hypothesis about the relevance of snake detection processes: Snake phobia, and not spider phobia, was found to be related to perceiving vertical pupils as threatening (Study 5), however an experimental manipulation of saliency of snakes rendered no significant effect (Study 6) and a comparison of fears of snakes, alligators, and cats did not support our prediction (Study 7). We discuss the potential implications and limitations of these novel findings.