Pythagorean cup

Our tourist guide in Greece showed us this particular thing... And it fashinated us so much!! Watch the video, that is worth a thousand words.It seems a simple mug, but there is a trick: if you fill it till a certain level, no problem, you can taste your drink; but if you are greedy and you want to fill it till the top... the mug rips off you, and it becomes completely empty.Its name is Pythagorean cup... in Greece you can find lot of cups with somthing like a pin inside it.this mug is even better: no pin inside, but it works too!! Can you guess how it works? Attention!!! The supports are not to be put in the handle, but only is at most on the lowest part of the cup!!!