A snake does not have lags so it derives momentum by pressing its underside on the ground. It curls its long body and then pressing the ground with its tail stretches its head and lungs forward. It goes on repeating this process to cover distance. Moving forward in this manner, an African snake called Mamba can achieve speed of 18 to 20 kilometers per hour. Of course the ground should be somewhat rough because snake’s belly is smooth. If the ground also happens to be smooth than it might slip for want of grip and will not be able to cover any distance. It is due to this reason that a snake becomes almost immobile on the smooth surface of glass.
Snakes of sandy desert would have found themselves in a sad plight for another reason. Minute grains of desert sand constantly slip underneath so it is not possible for the snake to move forward by pressing its tail in sand. On the contrary, when lunging forward it will only succeed in making a furrow in the sand. It will only get bogged down in the sand instead of moving forward rapidly. Another important factor: Unlike mammals or birds, snakes are cold-blooded reptiles whose body temperature does not remain at a constant level (E.g. body temperature of human beings remains steady at 96.6º Fahrenheit). Snake’s blood becomes cool or warm according to the temperature of the atmosphere. If a snake remains on the burning hot desert sand even for a short time its body temperature will rise to such a degree that it might die. So it shelters under a shade during hot daytime. If it has to move on the hot sand it has to keep as much of its body raised above the sand as possible and for as long as possible. It can avoid the heat of sand only if it is able to cut off the body contact with sand frequently.
To overcome both these problems desert snakes moves sideways. (See picture above.) Having selected the direction of its journey it positions itself at an angle of 60 degrees from it. Thereafter it propels sideways by pushing against the sand. As the snake is fully stretched its weight and consequently the force of its lunge is distributed all along its length so the sand under its body does not slip. Snake starts moving forward by a series of sideways leaps solving both the problems simultaneously. A snake is able to travel left or right in this sideways manner and not only that but thanks to its leaping gait its body does not have to remain constantly on the burning hot sand. The most famous snake known for its peculiar sideways curving or winding gait is sidewinder – and it is also the name given to a well-known guided missile of the USA.
List of snakes (Wikipedia)