Dripping water on a restrained person's forehead can eventually drive them insane.

The popular term for this type of abuse is "Chinese water torture," though there is no evidence that this method was ever used in China. The popularity of the term may have come from a stunt performed by Harry Houdini called the "Chinese Water Torture Cell" This trick involved Houdini escaping from a locked box overflowing with water.

It may also have come from Sax Rohmer's Fu Manchu stories, which were popular back in the 1930s. In these tales, the evil Fu Manchu would subject his victims to various inventive tortures. Or it may have just been simply called \"Chinese\" because it was intended to sound mysterious and foreign.
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The \"MythBusters\" team did an episode featuring chinese water torture! Check it out: