From Maze Solving by Chemotactic Droplets in the Journal of the American Chemical Society:
Droplets emitting surface-active chemicals exhibit chemotaxis toward low-pH regions. Such droplets are self-propelled and navigate through a complex maze to seek a source of acid placed at one of the maze’s exits. In doing so, the droplets find the shortest path through the maze.
I don’t generally understand materials science (or even much chemistry, for that matter), and this I really don’t get. How do it know?