The Assassin's Teapot

The physics of the Assassin's Teapot.  As Jason Kottke explains:

The teapot in question has two separate chambers for holding liquid, and the flow out of the pot from each chamber can be controlled by covering or uncovering small holes located on the handle. So, as the legend goes, a would-be assassin could pour themselves a perfectly fine drink from one chamber and then pour a poisoned drink to their prey from the other chamber, just by discreetly covering and uncovering the proper holes with their fingers. As the video explains, the mechanism here has to do with surface tension and air pressure.