mikejuk writes with an intriguing description of AquaTop, a (very) interactive display system developed at Tokyo's University of Electro-Communications Koike Laboratory, which uses a Kinect sensor, a projector, and a tub of cloudy water. Images are projected into the water, and as a user, "[Y]ou can move them around, resize them using the usual two-finger pinch, but you can also pick them up in cupped hands and transfer them somewhere else. The gesture I really liked was 'sink to delete' — yes, that's often how I feel about a file. Add some waterproof loudspeakers under the surface and allow the computer to run them at low frequency. The result is that you can now make the surface 'boil' in response to the sound. You can make fountains of water appear and project the right colors onto it to make it look like an explosion. In the demo game you throw energy bolts at squid that blow up if you hit them. You have to see the video to understand how putting your hands in cold water might be so much fun."