Look a little closer
Wombat droppings are not shaped by a square opening or pressed into molds after leaving the body. They dry while moving slowly through the final intestine, where walls of unequal elasticity repeatedly form flat faces and corners.
Wombats take a long time to digest tough vegetation. Water is removed as material travels through the gut, making it firm; anatomical research finds the distinct shape develops within roughly the final 17 percent of the intestine.
When researchers stretched intestinal tissue, its circumference was not mechanically uniform. Some regions were thicker and up to about four times stiffer, so softer and harder sections deform differently under the same contraction.
Mathematical models show that a ring with alternating elasticity can squeeze soft contents repeatedly into four faces and corners. It is a cumulative process of movement, drying and asymmetric contraction, not one stamp from a pastry mold.
Why the trait evolved is less certain than how it forms. Wombats stack droppings on rocks and logs for scent marking, and cubes may resist rolling away, but that functional explanation remains a hypothesis needing more direct tests.
The work demonstrates that a soft tube can form angular objects without a rigid mold. Shapes produced by tissue mechanics and water movement may even inspire new ways to manufacture soft materials.
