TrueReel on Instagram: "The X post shares a 14-second video demonstrating a common "fingernail test" variant using a playing card against mirrors to detect two-way glass, showing no gap in reflection as a supposed red flag. - This method is a myth; it only identifies first-surface mirrors (reflective coating on the front, rare in homes) versus standard second-surface ones, per Snopes and Physics Stack Exchange analyses. - Accurate two-way mirror detection requires illuminating the mirror in dark