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.

Nojima, a graduate student in information science and technology at the University of Tokyo, is demonstrating how electronic sensors can make distinctions about the world far beyond what humans can do. The probe works by measuring the change in electrical conductivity between the oil and the water. That data is sent to a PC that analyzes the information and then directs a controller to restrict the probe’s movement.

Such technology could guide a scalpel along the boundary between cancerous and healthy tissue. Nojima has already used it to build a knife that can cut through the white of a boiled egg without nicking the yolk. Other projects in the works include a flexible touch sensor to give robotic fingers the same tactile sensitivity as human digits.