Undulatory locomotion
From Soft-Matter
Definition

Schematic of lateral undulation locomotion for a snake (the black dots indicate the location of inflection points and the thick line illustrate the pattern and amplitude of muscle activity. (Limbless undulatory propulsion on land (Guo & Mahadevan 2008).
Undulatory locomotion is movement via propagating waves with the most tangible example being that of limbless creatures (e.g. snakes) on land or water. The lateral (side-ways) forces brace the animal's body (the motion in each lateral direction cancels itself out) against the substrate thus allowing the in-plane forces to propel it in a forward. Viscoelasticity plays an important role both in the mechanics of the muscular tissue and how the animal's body responds to its environment.