Wombats are the only animal that poops cubes

Wombats are the only animals known to produce cube-shaped poop. The secret is not the anus but the intestine. Researchers found wombat intestines have periodic stiffness, stiff-soft-stiff-soft along the circumference to form cubical faeces. Because wombats are nocturnal with poor eyesight, they poop in communal latrines to mark territory, and square poop stays put rather than rolling away. They then stack the cubes as scented signposts. The flat sides ensure the poop doesn't roll away, acting like organic bricks. Evolution turned digestion into architecture.