How to distinguish a double mirror

1, the finger touches the mirror. If there is a gap between the finger and the reflective finger, it is a one-sided mirror.

2. Look in the mirror with a flashlight. If it is a double mirror, the light can see the back through the mirror.

If you can't wear a mirror, it's not a double mirror.

3. You can also hold a hole in your hand and look close to the mirror. You can see the opposite mirror, but you can't see the single mirror.