Ask a child to draw some poo, and the shape will invariably be the same: a coil, broad at the base and pointy at the top, similar to a spiral swirl of soft-serve ice cream. In fact, the often-used poo emoji has this exact shape, as do most actual mounds of feces found in nature. Exceptions occur, though, particularly in the feces of some worms that extrude their excrement “upside down” from the ground. As it turns out, there is remarkable physics behind these differences in poo shapes.