Artificial terrace patterns and molluscan shells were dragged on and within sorted sandy sediments, and the differential force necessary to move in the forward versus backward direction was measured. As expected, terraces display different frictions when moving in opposite directions. However, no obvious relationship in frictional properties emerged between the studied ranges of terrace heights and sediment grain-sizes. Rather, friction is affected by the shape of sediment grains. Terraces with a very low inclination of their leading sides are more effective than terraces of similar height but with steeper leading sides, in spite of the closer packing of terraces allowed by the latter character. Experimental results appear to be considerably influenced by minute changes in sediment compaction (especially in water-permeated sediments), depth of burial, and orientation of the test objects. □Burrowing sculptures, fiction, functional morphology, experimental biology, biomechanics.