Begin by placing the tip of your fingernail against the mirror. If you see a GAP between your fingernail and the mirror, you’re safe, it’s a genuine mirror.
If there isn’t a gap, and your fingernail is directly touching your reflection, there’s a high possibility it’s a two-way mirror.
Remember: “If there’s no space, leave the place”
The next time you’re unsure if you’re looking at a mirror, use this simple test and you’ll know within seconds!
source : http://alfstories.com