Electronic sensors can make distinctions about the world far beyond what humans can do.
Takuya Nojima picks up a cocktail stirrer and sticks it into a small pot that's half full of water, with a thick layer of oil floating on top. The stirrer slices through the oil and water mixture effortlessly, just as you'd expect. But then he lifts a pencil-like plastic probe dangling from the end of a mechanical arm and pushes its tip into the pot. It slices through the oil but stops dead at the water, refusing to penetrate.