Limbless animals generate and propagate waves along their body to move in complex terrains. Specifically, snakes rely on alternating unilateral muscle activation for locomotion [Jayne, J.Morph., 1988]. Previously studied desert specialist snake [Schiebel et al.,PNAS, 2019], C. occipilatis , relies on passive body buckling aided by unilateral muscle activation to negotiate and overcome obstacles. Inspired by those experimental results, we developed a robophysical model, measuring 63cm in length and 8cm width, that models snake muscle morphology and activation patterns. The robot consists of 8 joints, each composed of a two motor pulley system. Each joint is actuated by having a pair of motors on one side spool while the opposite side is completely unspooled generating no tension. Joints were programmed to be unilaterally active, propagating a sine wave along the body of the robot. We performed wall collision experiments, where the robot would collide head-on with a low friction surface. Upon collision, the robot passively buckled, similarly to the snake, causing an increase in the body wave amplitude and changing its orientation to resume motion. Further, we performed experiments in a hexagonal lattice, a simplified heterogeneous terrain. The robot exhibited two behaviors to overcome jams and traverse the lattice. As in the wall collision experiments, we observed passive buckling that allowed the robot to reorient itself and to progress around an obstacle. In addition, we observed a reversal behavior that allowed the robot to overcome jams when the nominal waveform was perturbed. Our results suggest that as in legged devices, obstacle negotiation in limbless locomotors can be enhanced by offloading control to mechanical design, without relying on external sensing of the environment.