Circles, slaloms, figure eights, and loop-the-loops – biologists studying the motion of Listeria monocytogenes sensed that these paths were related, but they didn’t have a good way to define what fit in and what didn’t. A remarkably simple new mathematical description, published online in the Proceedings of the National Academy of Sciences, reproduces all these shapes with just one pair of equations and only two key variables. Besides helping to identify bacterial mutants, the equations suggest which mechanisms could be driving the motion.