Wombats, short-legged, burrowing marsupials native to Australia, are the only animals known to produce cube-shaped feces. It’s long been speculated that wombats produce these poop bricks as a unique way of marking their territory. Now, scientists have determined the likely causes of these unusual feces are the shape and flexibility of the wombats’ intestines, National Geographic reports. Researchers inflated long balloons in the intestines of dead common wombats to measure the shape and flexibility and found two ravinelike grooves where the intestines were more elastic. These grooves could form the poop into a solid cube just before it exits the wombat, the scientists reported over the weekend at the annual meeting of the American Physical Society’s Division of Fluid Dynamics in Atlanta. Next, the researchers say they’ll investigate how only two intestinal grooves can extrude a cube, as opposed to four—one for each face except the top and bottom.