This animation shows a long and narrow channel (notice the values on the horizontal and vertical axis) full of self-propelled particles (bacteria) with excluded volume interaction. The dashed line in the middle of the sample represents an asymmetric obstacle. Notice that even if the sample is initialised homogeneously, eventually the self-propelled particles break the symmtery, flowing into the right compartment. The simulations carried with this framework show complete agreement with the experiments in vivo performed at Princeton by Austin et al. on bacterial colonies.