Snake
Terrestrial lateral undulation is the most common mode of moving for most snake species. In this mode, the posteriorly moving waves push against contact points in the environment, such as rocks, twigs, irregularities in the soil, etc. The movement is just the same over sand and in water. The movement makes a force against the substrate (ground, sand or water). This gives forward thrust. The speed of the movement depends upon the density of push-points in the environment. The wave speed is the same as the snake speed, and as a result, every point on the snake's body follows the path of the point ahead of it. Snakes move through dense vegetation, small openings, sand and water all quite well.