Click the green flag. The particles start at random positions up high (colored red) and move down until they touch a stationary particle (colored green). Coral like, fern-like patterns appear.
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 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. In NetLogo, we were able to give much more control: https://lifepatternsemerging.com/wp-content/uploads/2020/11/DLA-additive-stickiness.html
