Sidewinding

Any number of caenophidian snakes can be induced to sidewind on smooth surfaces, though the difficulty in getting them to do so and their proficiency at it vary greatly.

A picture of a snake performing lateral undulation would show something like a sine wave, with straight segments of the body having either a positive or negative slope.

Sidewinding is accomplished by undulating vertically as well as laterally, with the head tracing out an ellipse in a vertical plane nearly perpendicular to the direction of movement and with all the segments that have a significantly non-zero slope (and alternating segments that have a zero slope) lifted off the ground.

[1][2] In the resultant movement, the snake's body is always in static (as opposed to sliding) contact when touching the ground.

Implementing this control scheme in a snakebot capable of sidewinding allowed the robot to replicate the success of the snakes.

Sidewinding in a newborn sidewinder rattlesnake. Yellow regions are lifted above the sand and in motion at the time of the photo, while green regions are in static contact with the sand. Blue denotes tracks. Scale imprints are visible in the tracks, showing that the snake's body is static during ground contact.
Tracks of a sidewinder in the sand.
A crude animated line-drawing showing the locomotor pattern of sidewinding. The light brown areas are the tracks left behind, and also indicate where the body of the snake touched the ground.