The builders of Japan’s Nijo castle created purposefully squeaky floors, known as nightingale floors, to prevent ninja assassins from sneaking in. The floors were designed so that just the lightest step produced a clearly audible sound warning guards. – WTF Fun Facts
Source: https://www.amusingplanet.com/2018/04/nightingale-floor-ancient-japanese.html
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WTF Fun Fact – Slippery Escape
In 2012, Choi Gap-bok escaped from prison by squeezing his body through a 5.9″ tall and 17.7″ wide food slot when the guards were sleeping. He is a yoga practitioner and applied skin ointment to his body in order to slip out. – WTF Fun Facts
Source: https://www.huffpost.com/entry/choi-gap-bok-prison-escape_n_1919866