This model works on the same principal as the original assassins teacup just maybe a little less convincing (which is probbably a good thing and makes it just a very cool toy to play with) due to its weird shape and the fact that it only has one chamber. When you leave the cover at the back open and simply pour water down it will go to the back and settle as air can be pushed out the hole after putting water in assuming you actually want to pour the drink the hole needs to be open and water will come out if you plug the hole air wont be able to come replace the water creating a vaccum stopping you pouring the drink. Essentialy you can control wether or not anything is being poured or not.