Multiple Walter Whites will walk the streets on Thursday in search of candy. But some frights endure the fashion cycle and never go out of style.

This week in Proceedings of the National Academy of Sciences, a team of scientists examines one particularly long-lasting source of fear: snakes. The researchers found that certain neurons in the brain only respond to these legless reptiles. These snake-dedicated neurons, they argue, are a legacy of our distant primate past, when the animals posed one of the greatest threats to our survival.

The new study builds on years of experiments by psychologists. They found that the widespread fear of snakes stems from a perceptual bias: people recognize snakes faster than other objects.

This bias toward snakes isn’t simply the result of learning to fear them. Children recognize snakes just as quickly as adults. In a study published earlier this year in Developmental Science, psychologists found no difference in the response to snakes when they compared children who grew up in cities with children who grew up in rural areas where they regularly encountered snakes.