Crucially, the researchers did not pre-rate the images or assume which animals would seem frightening. Instead, they grouped participants' ratings statistically and then checked whether each group lined up with specific visual traits.

"Three clear groups emerged," Soares said.

Shape matters — but not perfectly

Vipers and several boa species were linked with higher fear and arousal. Several slender colubrids and dipsadids — a large family of mostly harmless snakes — were viewed more positively. Smaller fossorial snakes, which live underground, along with some non-snake limbless reptiles, tended to elicit disgust.

These patterns did not simply track real danger, the researchers found. The visual cues appeared to guide people's judgments even when they had no idea how venomous a given snake was.

"These cues may therefore work together as a kind of visual threat heuristic: the perceptual system may use aspects of an animal's appearance as a shortcut for evaluating potential danger," Soares explained. That shortcut, she noted, could explain why harmless species that resemble more threatening snakes are often perceived as highly threatening.

"From an evolutionary perspective, this is consistent with a perceptual system that favors caution over perfect accuracy when the potential cost of failing to recognize a genuine threat is high," she added.

Appearance alone, however, did not fully explain the responses. Fearful reactions were also strongly shaped by participants' reported encounters with snakes and their general level of snake fear. Greater exposure to natural environments was associated with lower self-reported fear, though the study cannot show that exposure itself causes the difference.

"Visual characteristics seem to help structure which snakes are perceived as relatively threatening, while individual factors help determine the intensity of that response," said Soares. Together, she argued, the findings point to an interplay between shared perceptual biases and individual experience rather than a rigid, entirely innate fear response.

Beyond fear

The study also reinforces the idea that human reactions to snakes cannot be reduced to fear. Fear and disgust turned out to be distinct responses, and neither mapped neatly onto beauty: a snake perceived as threatening or disgusting is not necessarily seen as ugly.

"The same animals can evoke fear or disgust while also being perceived as beautiful and becoming powerful objects of human fascination," Soares said.

The team's next steps include isolating individual visual features — shape, scales, texture, patterning — to see whether any of them alone can influence responses when visual information is limited. They also plan to use eye-tracking and EEG (a technique that records the brain's electrical activity) to trace how a snake image moves from detection to attention to conscious emotion, and to compare reactions to snakes with perceptions of predators such as felids and raptors.

More than 20 years ago, in their paper "The Malicious Serpent," researchers Arne Öhman and Susan Mineka asked which visual features make snakes such powerful triggers of fear and attention. "We would like to take up that challenge, but also go beyond it," Soares said.

As with any single online survey, the findings are preliminary: they describe associations, not causes, and the participant pool covered only two countries. Still, the results offer a concrete step toward understanding why snakes — harmless or not — hold such a strong grip on the human eye and imagination.