Challenge: Describe in words why when you look in the mirror your left and right sides have flipped but not the top and bottom. But when you lie down horizontally, what side was on the bottom is now on the top. As if the top and bottoms have flipped.
This demonstrates that words can generate a paradox when there is none. Why is it that in one case the mirror flips horizontally and in another case, it flips vertically? How does the mirror know when and how to flip the image?
Words are instructions of imagination. It is like a magic trick when words distract you from the solution of the problem. Why does a mirror flip an image vertically or horizontally depending on a person's reference frame?
Zeno Paradoxes are a collection where the listener is instructed to imagine a reference frame that leads to a paradox when there is none in an appropriate reference frame. en.wikipedia.org/wiki/Zeno%27s_…
A person cannot actually tell the difference between an image in a mirror and an actual image unless there is an object in the image that has a known asymmetry of left and right.
A mirror flips what is left and what is right independently of how you look at the mirror. It does not matter if you are lying down or standing up. This is still not an adequate explanation though!
That's because when you look at the mirror from one side, you don't appear on the opposite side. You still appear on the same side of the mirror. It is not flipping left with right, it is doing something else.
It becomes obvious as to what is happening when you look into an infinite mirror. 
What a mirror does is that it changes the direction in how a 3D space is viewed. So as you face the mirror, an image of you is facing back in the opposite direction.
This is a very subtle thing that even this video doesn't actually mention the word direction.
This video does a better job by explaining that direction if flipped.
Direction is related to rotation. So when a mirror flips the direction of how a 2D image is facing, it does so by also change the direction of rotation. A clockwise rotation appears counterclockwise in a mirror.
Riddle: When do clock hands rotate counterclockwise? Answer: When viewed from a mirror.
The moral of the story here is that something appears subjective when looked at from the wrong reference frame. 2D beings cannot imagine 2D mirrors.
It's also interesting that to imagine how something looks in a mirror you can just imagine looking at an object from the inside out. This is the opposite direction of how we usually look at objects (i.e. from the outside).
@threadreaderapp unroll
This brings the strangest analogy is that it captures the notion of empathy. That is, to understand someone is to look at oneself in the mirror. That is, to see yourself from the inside.
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