Out in Finland, where the days are long and the ice is plentiful, a team of Nokia researchers went ahead and made a touchscreen out of ice. Why? Why not?
They took big cubes of ice, polished them with a heat gun and then beamed through them with a near-infrared light source. They then used some computer tracking to see where people's hands were and voila, an ice touchscreen.
There are no real practical uses for such tech, but it's nice to know it's possible, isn't it?