Snakes have been on the earth for 70 million years. That is a long time. Some reaching 50 to 100 feet in length.
Their sense organs are uniquely different than those of other animals. Unlike mammals, snakes rely primarily on their senses of smell and touch. They do not have moveable eyelids, but transparent caps called “brille” as protective eye coverings. Because of this, their eye movement is fairly limited. They also do not have an external ear, middle ear, or tympanic membrane (eardrum). Instead, they use a small ossicle (ear bone), called the “columella,” to detect vibrations of sound waves conducted through the ground. They are able to pick up some sound waves conducted through the air, but only at very low frequencies.
Snakes also smell in a different way. Mammals bring air particles into contact with the olfactory (smelling) nerves by breathing them into the nasal cavities through the nostrils. Snakes have both nostrils and nasal cavities, but they are not used to smell. Instead, the flicking tongue is actually a smelling device. There is a small organ on the roof of the oral cavity called the “vomeronasal organ”, or “Jacobson’s organ.” The forked tongue is used to bring minute air particles into contact with this organ, and the snake then perceives and identifies the smell as prey, predator, or otherwise. So, unlike mammals, the tongue is not used to taste or aid in swallowing, but simply as an accessory smelling organ.
Some snakes also have a “sixth sense”. Vipers, rattlesnakes, and other members of the family of snakes known as the ‘pit vipers’ have special pits located between their eyes and nostrils. The pits are used to sense minute temperature changes as infrared rays, as an aid in locating warm-blooded prey such as rodents. A pit has two chambers. The interior chamber is naturally the internal temperature of the snake itself. The exterior chamber heats up when it is close to a heat source, and the snake is then able to detect the temperature difference between the two chambers. This system is so accurate that pit vipers are actually able to detect temperature changes as little as 0.002° Celsius.