Im siebzehnten Jahrhundert bauten sie in Japan Alarmanlagen gegen Ninjas in ihre Böden, so wie das in den Zeichnungen und Videos aussieht flächendeckend, ein bisschen wie'n vintage Sensor-Boden gegen Ninjas. Whoa!
In 16th-Century Japan, rumors of ninja prowess began to spread. And by the 17th Century, clever castle-builders designed a countermeasure to alert sleeping residents if there was a ninja sneaking around. The design feature was called uguisubari, or "Nightingale floors." When one walked over the floorboards, this precise noise was produced:
The builders achieved this bird-like noise by placing metal against metal. Beneath the joists, they mounted extraneous metal brackets with nails driven through them.