The ball I'm holding at right is one of the demo units. It's technically not a product because E-ink don't actually sell it. But it is very cool, isn't it?
The ball represents one of the capsules of an E-ink screen. The little black and white dots floating in the clear liquid represents the pigment micro capsules. I'm not going to go into a long technical explanation how it works, but I will direct you to a complicated and technical explanation on Wikipedia.
This little ball is even more fun to hold than it is to watch in the video, and it's a testament to the value of having a prop. This little ball is the main reason TechCrunch (and probably other sites) posted the interview.