If there’s a gap between your nail and the mirror, it’s most likely a genuine mirror. But if you place your fingernail up to the mirror and it appears that your finger is directly touching the finger in the mirror, you might want to investigate further. It might not be reliable. Another way to check is to Sound it out. Tap on the surface of the mirror. A normal mirror will produce a dull, flat sound, while a two-way mirror will sound hollow and metallic.
