Long before the modern lie detector and its harmlessly jittering graphs and wires were invented, the untruthful faced a much more severe fate between the jaws of the Bocca della Verità, or Mouth of Truth (or Mouth of Fate), an ancient carving that is said to bite the hands off of liars.

While no one is exactly sure when or why the frieze was created, there are a number of theories. Dating back to about the first century A.D., the Mouth of Truth is a tall stone disc carved with a humanoid face that has holes for eyes and a gaping mouth. The original purpose of the large medallion has been theorized as everything from a ceremonial well cover, to a piece of fountain decoration, to a manhole cover. 

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Source: http://www.slate.com/