system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] When staring at any object in the dark, the small details on it seem to look distorted and move around. What’s the explanation behind this?
gpt
The way that vision cells (rods and cones) work in your eyes is that if a photon interacts with a chemical substance within them, it causes a chain reaction which causes a nerve signal to be sent to the brain. The more often this happens per second, the brighter it seems to us. This is a random process though, and if there's just very little light to see, the chain reaction happens so rarely that things can randomly appear brighter for a split second. 

The distrtion comes from the fact that in the center of our field of vision, there are mostly cones, which can see color but aren't that sensitive to light. On the outside, there are mostly rods, which can't see color, but are much more sensitive. So if it's dark outside, the cones in the middle become fairly useless, and you see mostly with the rods on the outside. The distortion comes from our brain trying to make sense of an image with a black hole in the center.