In 1984’s A Nightmare on Elm Street and its numerous sequels, Freddy Krueger typically prepares for a round of trademark depravity by donning a red- and green-striped sweater. The details of this routine are a little foggy. Perhaps his dreamworld drawers are bursting with identical sweaters to ensure he has a clean one for each murder spree; or maybe he owns a single sweater, which he only throws on when there’s slashing on his schedule. Either way, if the classic killer shows up in your neighborhood, you can bet he’s decked out in red and green.

Since those two colors so often evoke images of Christmas, the sight of them in such a terrifying context is definitely unsettling. But director Wes Craven wasn’t trying to be subversive when he chose to clothe his villain in holiday hues—he was trying to make us uncomfortable in a much more subliminal way.

According to ScreenRant, Craven landed on the color scheme after reading in a scientific article that humans have an especially hard time processing the colors red and green together. As Live Science explains, red light causes retinal cells called opponent neurons to fire—thus alerting our brain that we’re seeing red—while green light doesn’t cause them to do anything (a lack of motion that our brain knows to perceive as green). Since these actions cancel each other out, seeing certain shades of red and green simultaneously can be a little optically confusing.

The same phenomenon happens with yellow and blue, so we’d probably be just as unnerved if Freddy Krueger was dressed like the IKEA logo of our nightmares.

A version of this story originally ran in 2020; it has been updated for 2023.

This article was originally published on www.mentalfloss.com as The Smart—and Scientific—Reason Freddy Krueger’s Sweater Is Red- and Green-Striped.