Question

why there is only vertical flip in mirror

Answer 1

Here is your answers.

Because, you see, the reason that things appear to always be flipped horizontally in the mirror is because we flip them horizontally. Try holding up that "Food" sign again, but then flip it vertically to face the mirror, and then you'll see an upside down, but forward facing, "Food" staring back at you.

Hope it helps you.