Snakes can bend their elongate body to traverse complex 3-D terrain. With the exception of sidewinding with small vertical body lifting, most previous studies of terrestrial snake locomotion used flat surfaces and focused on the role of lateral bending. Few studies tested terrain with large height variation or considered whether snakes can use vertical bending to traverse. Recent studies in our groups revealed that snakes use vertical body undulation to traverse a horizontal cylindrical array (Jurestovsky et al., in prep) and combine lateral oscillation and vertical bending to traverse a large step (Gart, Mitchel, Li, 2020, JEB). Here, we hypothesize that generalist snakes bend their body both vertically and laterally to traverse complex 3-D terrain. We tested corn snakes Pantherophis guttatus (N = 2 animals, n = 23 trials) traversing low-friction, rugged terrain comprising blocks of normally distributed heights. Despite the low friction, the animal traversed stably with little slip as if it were moving in a tube, with frequent changes in head direction. In addition, the animal tended to move on top of lower blocks, as if it were going through a valley in the rugged terrain. On these lower blocks, the body bent vertically to push backward against horizontal ridges to propel forward. Although lateral bending was occasionally used to push against the side of higher blocks, it was not sufficient to explain the observed motion. These observations supported our hypothesis. To better understand how the animal controls 3-D body bending to traverse, we are developing a sensorized terrain platform to measure distributed ground reaction forces and a sensorized snake robot as a physical model for systematic experiments (see other talk: Ramesh et al., A sensorized robophysical model to study snake locomotion in complex 3-D terrain).