The sandfish lizard uses body undulation to swim within sand (x-ray image, left), a granular medium in which frictional forces dominate the dynamics. Numerical simulation (right) consisting of a multibody simulation of the animal coupled to a multiparticle model of the granular medium (several hundred thousand 3 mm–diameter glass spheres) allows investigation of the mechanics of swimming, including resistance forces and power consumption. In the right panel, a localized region of grains around the simulated sandfish is fluidized (brighter color indicates faster motion), while the grains only a body width away remain in a solid state. See Ding et al.

Image Credit: Yang Ding, Sarah S. Sharpe, and Andrew Masse, Georgia Institute of Technology.