Scientists used an X-ray to understand how desert animals move through sand, and how that movement shaped their bodies over time. Turns out the trick, for the animals, was making their bodies wave, while leaving the sand undisturbed.
Researchers at Georgia Tech compared the motion, and efficiency, of shovel-nosed snakes and sandfish lizards. Both "swim" through the sand instead of moving over it. And both move using only the motion of their body. (The lizard doesn't use its limbs when it's under the sand.)
How do they move? The shovel-nose snake begins by thrusting its head forward. Then it propagates a wave along its body from the head down to the tail. This allows it to move through a kind of "tube" in the sand created by its head. Its motion, its elongation, and its slick skin leave the sand around it relatively untouched. The lizard is shorter. It disturbs more sand, which causes it to slip more often than the snake does.
According to Dan Goldman, a professor at the school of physics:
For each body wave the snake generates, it moves farther than the sandfish does within a single wave of motion of its body. Having a long and slender body allows the snake to bend its body with greater amplitude while generating more waves on its body, making it a more efficient sand swimmer.
At around the thirty second mark of the video, you can see a long clip of the snake moving fluidly under the sand.