There are a lot of similarities between the popular home robot and the forest-floor goop you wish you hadn’t stepped in. Following a combination of programmed cues, an iRobot Roomba responds to its environment, detecting dirt and vacuuming it up. Slime mold, or Physarum polycephalum , functions in a similar way, behaving in accordance with a list of genetically inherited rules. It’s a simple, single-celled organism that digests detritus and leaves behind a trail of slime wherever it goes. What makes slime mold remarkable is that when threatened, all the individual cells in the area combine, creating a larger organism—a collective entity capable of solving problems that a Roomba would find challenging.