Snakes are one of the world’s most versatile organisms, at ease slithering through rubble or climbing vertical tree trunks. Their adaptations for conquering complex terrain thus serve naturally as inspirations for search and rescue robotics. In a combined experimental and theoretical investigation, we elucidate the propulsion mechanisms of snakes on both hard and granular substrates. The focus of this study is on physics of snake interactions with its environment. Snakes use one of several modes of locomotion, such as slithering on flat surfaces, sidewinding on sand, or accordion-like concertina and worm-like rectilinear motion to traverse crevices. We present a series of experiments and supporting mathematical models demonstrating how snakes optimize their speed and efficiency by adjusting their frictional properties as a function of position and time. Particular attention is paid to a novel paradigm in locomotion, a snake’s active control of its scales, which enables it to modify its frictional interactions with the ground. We use this discovery to build bio-inspired limbless robots that have improved sensitivity to the current state of the art: Scalybot has individually controlled sets of belly scales enabling it to climb slopes of 55 degrees. These findings will result in developing new functional materials and control algorithms that will guide roboticists as they endeavor towards building more effective all-terrain search and rescue robots.