>>10861733A mirror doesn't flip images across a vertical axis. It doesn't really flip anything. Each part of the mirror reflects what's in front of it.
Let's say you're in front of a mirror. Between you and the mirror is a piece of paper. You take out a marker and write, on the side of the paper which faces you, the lower-case letter "p". Now, what do you see in the mirror? Well, you just see the opposite side of that paper, which is blank. Let's say you want to look at the letter in the mirror. What do you do? You turn the paper around.
But how do you turn the paper around? Well, if the mirror were a person, you'd flip the paper around so that the letter is in an upright and thus readable orientation. That's the default way of turning anything with writing on it. So when you turn the paper to face the mirror, you probably flip it about the vertical axis so that the bottom of your letter "p" is still pointing downward.
But now the right side of your letter "p" (though you can't see it through the reverse side of the paper) is on the left. You see "q" in the mirror, but it's not because the mirror flipped the paper about the vertical axis; it's because you did. Replace the paper in this experiment with a piece of glass, and you see "q" not only in the mirror but through the reverse side of the glass.
If you had flipped the letter about the horizontal axis, you would see "b" in the mirror instead. If you had written the letter on glass and not flipped it at all, the letter you would see in the mirror through the reverse side of the glass would still be a "p".
