Offscreen, there are good reasons why so many kids (and some grown-ups) are scared of the dark: Our eyes really do play tricks on us. “There are so-called optical illusions, which help illustrate that there are actual physical and chemical processes that underlie vision,” Brodie says. “In the dark, the retina is just as active, more or less as in the light,” Brodie says. “The bottom line is that there’s noise in the visual system, which becomes a predominant sensation in the absence of light,” Brodie says. It’s worth noting that there are other factors beyond our visual system that may make it feel like there’s something out there in the dark.