Gazing into a remarkably detailed digital eye did not stir up latent fears of the omnipotent. At least, that wasn’t the case with the all-seeing eye that I recreated with the Eye Texture Raytracer, a WebGL project that lets you manipulate the dimensions of a digital eyeball in alarming detail.

After staring off into the Eye of Sauron for about 10 minutes, I was awash with a profound sense of the creeps. But I was also gifted an excellent lesson in pupil dilation, an equally mysterious but less morally revelatory subject.

The Raytracer eye is incredibly realistic. A single bloodshot sphere floats on a background of your choice (I chose “Circus,” a lifelike, entrail red) At the center sits a striated, sea-green iris. Yet it was the jet-black pupil, contracting and relaxing with the calm regularity of a breath, that made me feel weird as fuck.

It didn’t take me long to realize why: Pupils don’t move like that. Dilation is a physiological response, which means the eye needs something to respond to. If this Eye were really gazing back at me, it’d probably contract here and there as it tried out different modes of focus on me — a new stimulus — before settling on something in between. But this eye is dilating constantly, which suggests the unnerving possibility that it’s pointed at you, but not looking at you — perhaps because it’s gazing at something else, something that’s stimulating it with terrifying regularity and is exactly where you are.

Scientists still aren’t sure what makes a pupil dilate. They used to think the pupil was solely a visual tool, like a camera lens, that adjusted to how much light entered the eye. It’s obvious now, though, that pupils respond to arousal in general (and not just the sexual kind). Sure, in Sherlock, the titular detective calls out ice queen Irene Adler on her latent crush by observing her pupils dilate as he comes close; but studies have shown that the same thing happens when students are asked to solve difficult math problems.

Dilation is, essentially, the body’s way of betraying the mind, as The Scientist so aptly describes:

“Scientists have since used pupillometry to assess everything from sleepiness to introversion, race bias, schizophrenia, sexual interest, moral judgment, autism, and depression. And while they haven’t been reading people’s thoughts per se, they’ve come pretty close.”

The opposite of the Raytracer’s eye is one that appears completely static; that is, one that doesn’t seem to be responding to anything. Hip-hop group Dilated Peoples, according to Genius, is named after the effect of dropping too many hallucinogens. Others have painstakingly documented how certain drugs — ketamine, coke, LSD, to name a few — turn pupils into endless black holes, most likely because it’s a lot harder to be visually stimulated when you’re already so turnt.

I lost my staring contest with this eye before it even began. Even without the flames of Barad-dûr, this facsimile of Tolkien’s Eye was still pretty upsetting, less so because of its gaping form but what that gaping form implied. Eventually the regularity of its opening made me feel like I was staring into the maw of some sick undulating creature, like a giant squid, as it slowly decided how best to visually suck me — or whatever it thought I was — in. I looked away.