This diagram demonstrates the workings of:  

A.

The idea of this ancient prank is deceptively simple: if you pour a moderate amount of wine in the cup, you can drink without incident. But if you pour above a certain point, the wine will all drain out through the stem before you’ve even had a sip. While it’s difficult to know for sure who the creator of this devious drinking vessel was, most scholars agree it was Pythagoras, the ancient Greek philosopher and mathematician who lived between 570 and 495 BCE. According to one legend, Pythagoras created the cup to punish his peers who greedily over-filled their cups of wine. Other theories suggest that he wished to remind people to drink in moderation. The design of the Pythagorean Cup features a small column in the middle of the cup’s bowl, directly over the hollow stem of the cup. The column conceals a U-shaped chamber leading from a hole at its base in the cup bowl, to the bottom of the stem. As the cup is being filled, the level of wine in both the bowl and the column rise equally. When the cup is filled beyond the height of the column, a siphon is created, pushing the wine from the cup into the column and out through the hole in the stem, draining the entire cup. Whew!