Finger-like structure flow

Dissolution in topologically constrained media gives rise to fractal fingering, Figure 6.8 B (cf. also figures in [201,204,205]). The tree-like structure shown here indicates the flow of liquid where dissolution takes place. 

Try smacking the spoon down on the oobleck, and then try picking up the oobleck in your hands. It feels fairly solid when you pick it up and squeeze it, but if you hold it in the palm of your hand, it appears to melt into a puddle and you can drip it between your fingers. Oobleck behaves in this manner—not quite solid, not quite liquid—because cornstarch traps water, somewhat like a sponge, but the structure of starch is less rigid so it can flow with its water load. 

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