Tim from Grand Illusions (which sells cool cabinet-of-curiosity style stuff) demonstrates the Assassin's Teapot:
This teapot comes from China, and it is a trick teapot! Inside there are two separate compartments, and depending where you place your fingers – either covering one hole or covering another hole – you can get the teapot to pour out of either internal compartment.
Supposedly, back in the day, it was a way to get rid of an enemy, since you could pour out some tea for yourself and drink it quite safely (provided you had covered the correct hole) and you could then pour a drink for your enemy, and they would unknowingly get what was in the second compartment, maybe poison.
I also like his demo of an "atomic trampoline":
