system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When you rub your eyes and see rainbow colors and swirling patterns what’s really happening?
gpt
Pressure can stimulate the cells in your eyes that usually respond to light. As a result, even though there *isn't* associated light, they fire off signals to the brain. 

The brain doesn't have any way of sorting 'light' signals from any other that come from those cells, so it just says "Ok, I'll paint the picture!" and creates an image based on what it receives.