Have you ever wondered how a mirror works? It flips things around from left to right, but why not from top to bottom? And if you lay on your side it flips your image from top to bottom, but not left to right. What's going on?
Kids love to play with mirror reversed letter and numbers almost as soon as they learn how to read, but most of us don't go much further. There are three levels of understanding what's going on. For the mirror imaging the first level is enough. I'm going to ask you to make your own simple demonstration to get to that aha moment.
You'll need an arrow. Something like this:
Cut one out of stiff paper or cardboard. I won't tell anyone if you want to be artistic.
You'll also need a very flexible reusable glove, the kind that you have to peel rather than slip off. Thin rubber, latex or something else. Again artsy is fine by me.
You'll also need a mirror to stand in front of. I'll wait...
OK.. hold the arrow to your right. Point it up towards the ceiling, down towards the floor, left and right taking note of what happens. Now try it with your other hand. The mirror is doing what experience tells you it would, but you have a nice label on the direction of the arrow.
Point it at the mirror and move it towards the mirror to where it touches. Then pull it back. Interesting, eh?
Glove up and point a finger towards the mirror. Pull off the glove and carefully watch what happens.
The mirror is flipping the image along the axis going into it. It pulls your image through itself.
That's it. The axis of symmetry for a mirror - its special direction - is your line of sight.
Going deeper and understanding how a mirror reflects light takes an understanding of electromagnetism .. Maxwell's equations. Deeper still, what's going on between light and matter, requires quantum electrodynamics. But they're overkill to understand why mirror images work like they do.