If you take a bucket of water balloons and jostle one of them, the neighboring balloons will respond as well. This is a scaled-up example of how collections of cells and other deformable particle packings respond to forces. Modeling this phenomenon with computer simulations can shed light on questions about how cancer cells invade healthy tissue or how leaves and flowers grow. But the behavior of cell aggregates is extremely complex, and fully capturing their structure and dynamics has proved tricky.