A wombat does not need a square opening to make cube-shaped droppings.
Dry material moves through intestine sections that stretch with 2 different kinds of stiffness.
Researchers modeling the gut found that alternating elastic and rigid regions can create flat faces and sharp corners near the end of digestion.
Those cubes are less likely to roll from rocks or logs where wombats leave scent marks.
That means the odd geometry is a gut-mechanics result. The cube is made before it leaves the animal.