The Pythagorean Cup by AstroMedia
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Drinking is a skill that requires practice: The Pythagorean Cup—also known as the Cup of Temperance or Tantalus Cup—is a drinking vessel that compels the user to drink moderately. Its ingenious design allows the cup to be filled only to a certain level. This allows the modest user to enjoy their drink in peace. However, if they are greedy and pour themselves over the fill line, the entire contents spill onto the drinker's lap.