The cubes in a wombat’s droppings are already there before they reach the exit. A 2021 study of bare-nosed wombats found cube formation in the final 17 percent of the intestine, ruling out the popular idea that a square-shaped anus does the molding.
The researchers found that the intestinal wall is not evenly flexible: some regions were about twice as thick and four times as stiff as others. Their measurements and model suggest that, as the intestine contracts, these contrasting sections move at different rates and create the flat sides and corners. The anus itself is round.
That makes wombat scat an odd example of a broader physics idea: a regular shape can emerge when a soft material is squeezed unevenly, without a rigid mold. The study gives a plausible mechanism for the cubes, but it does not settle why this shape evolved or what advantage it gives wombats.
The work was published in *Soft Matter* by researchers from Georgia Tech and the University of Tasmania. Read the [study abstract](https://pubmed.ncbi.nlm.nih.gov/33289747/) and the research team’s [wombat project page](https://www.hu.gatech.edu/Lee/cubed-poops/).
Image: 3D reconstruction from the [Hu Lab wombat project](https://www.hu.gatech.edu/Lee/cubed-poops/).
~science ~wombat
