system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do mirrors reverse left and right, not up and down?
gpt
Because the mirror actually doesn't reverse left right. It reverses _front and back_ - as if someone pulled your nose out the back of your head. If you track the image from the wall behind you, you'll notice that your back is closer to that wall than your nose is. However, if you extend this analysis to your image, you'll see that the nose of your image is closer to the (real) wall behind you than the back of your image. You've reflected front and back.