Despite their round appearance, the droplets you see here are actually shaped like little pancakes. They’re sandwiched inside a Hele-Shaw cell, essentially two plates with a viscous fluid between them. As these droplets fall through the cell, some remain steady and rounded (Image 1), while others experience instabilities (Images 2 and 3). By varying the ratio of the ambient fluid’s viscosity relative to the drop, the authors found two different kinds of breakup. In the first type (Image 2), droplet breakup occurred due to perturbations inside the drop itself. In the second type (Image 3), the viscosity of the ambient fluid is closer to that of the drop and intrusions of the ambient fluid into the drop break it apart. (Image and research credit: C. Toupoint et al.)