system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What causes you to see things out of the corner of your eye when nothing is actually moving or there?

Why do people have the sensation of seeing something moving out of the corner of their eye when there isn't actually anything there or moving?
gpt
There could be any number of factors for this. A common one is that despite the sense that your vision is steady and focused, your eyes are actually constantly moving and adjusting the field of view very subtly, and the differing images are compiled and averaged in your brain. Particularly sensitive areas of vision, such as motion of the periphery (which might have evolved to detect ambush predators such as wolves or great cats attacking from the sides), will be able to pick up the subtle shifts of your eye movements given the proper context or backdrop. 

Another contributing factor is that your eyes' contents themselves are not uniform. Small amounts of tissue can become dislodged in the jelly of the eye, and as it floats may cross in front of light entering the eye, which you can see as motes or "floaters". If one of these motes crosses the sensitive peripheral vision, the motion could also be detected.