Cracks Learn from Their Mistakes
A drying puddle of mud becomes covered with cracks, like an old painting with craquelure. At first the cracks meet at nearly right angles, forming a rough grid. But if the mud is wetted again and allowed to dry, the pattern changes: cracks begin to meet in threes, at an angle of 120 degrees, like a honeycomb.
Why this happens remained a mystery for a long time.