  Numerous animals live in, and locomote through, subsea soils. To move in a
medium dominated by frictional interactions, many of these animals have adopted
unique burrowing strategies. This paper presents a burrowing model inspired by
the Atlantic razor clam ({\it Ensis directus}), which uses deformations of its
body to cyclically loosen and re-pack the surrounding soil in order to locally
manipulate burrowing drag. The model reveals how an anisotropic body --
composed of a cylinder and sphere varying sinusoidally in size and relative
displacement -- achieves unidirectional motion through a medium with variable
frictional properties. This net displacement is attained even though the body
kinematics are reciprocal and inertia of both the model organism and the
surrounding medium are negligible. Our results indicate that body aspect ratio
has a strong effect on burrowing velocity and efficiency, with a well-defined
maximum for given kinematics and soil material properties.
