Click green flag. The particles start at random positions up high (red) and move down until they touch a stationary particle (green). Coral like patterns appear. Just for effect, we add a pen mark to each stationary particle. The color of new pen marks change over time. My wife drew the background so this is a husband-wife project.
A similar pattern is seen in crystal formation, coral, fungi growth, liquid seeping through soil, lightning, or what you see when you drop dye into glue, which is called viscous fingering. A process called diffusion-limited aggregation (DLA) happens to create the same patterns as seen in viscous fingering, in which a less viscous liquid presses through a more viscous liquid. The finger-like projections result from pressure being somewhat greater at the tips. We added a pen mark for color effect. Note that the pen size is smaller than the surrounding green clone. My wife Kathy did the background painting (part of our box on sea life ecology and coding). In NetLogo, we were able to give more control: https://lifepatternsemerging.com/wp-content/uploads/2020/11/DLA-additive-stickiness.html
