The Assassin's Teapot: How Does This Thing Work?

I'm struggling to figure out the physics here.This novel teapot of Chinese orgin has two chambers. You can see that when you look down the spout: So put regular tea in one chamber and poisoned tea in the other. Pour as needed.
Read more: http://www.neatorama.com/2016/02/17/The-Assassins-Teapot-How-Does-This-Thing-Work/?source=Snapzu