Now, I have three options that I would like to show you. The first one is mass. As humans, we are sensitive to where an object in our hand is heavy. So, could we use that in mobile phones? Let me show you the weight-shifting mobile. It is a mobile phone-shaped box that has an iron weight inside, which we can move around, and you can feel where it's heavy. We shift the gravitational center of it. For example, we can augment digital content with physical mass. So you move around the content on a display, but you can also feel where it is just from the weight of the device. Another thing it's good for is navigation -- it can guide you around in a city. It can tell you by its weight, "Okay, move right. Walk ahead. Make a left here." And the good thing about that is you don't have to look at the device all the time; you have your eyes free to see the city.