Coiling of lugworm feces reveals universal mechanics for the shape of poo

, in quantitative agreement with mechanical theory. This contrasts with typical downward defecation in most animals, which transitions from the gravitational regime to an elastic (kinematical) regime as the fall height to the top of the pile decreases. Our findings provide a quantitative mechanical framework for understanding fecal morphology and reveal how directional differences in waste disposal create fundamentally different buckling regimes across the animal kingdom.