Hint: It's Not For Talking
The fact is, the snake, and its tongue, have gotten a bad rap. A snake's tongue is one of the great marvels of nature; a cleverly designed appendage that gives the snake, one of the humblest creatures found in the animal kingdom, a much needed leg-up.
While there are other animals that have forked tongues, (some species of lizards, frogs and birds, for example), the snake has been found to have the most complex receptor system built into its tongue.
To begin, if you look into a snake's open mouth, you will not see much of a tongue at all. That is because most of the tongue is hidden inside of a sheath in the lower jaw when it is retracted, so that only the forked ends are visible. When the snake does flick its tongue, it passes through a small notch in the lip, called the rostral groove, which allows for the tongue to pass out of the mouth without the mouth having to actually be opened. You can also clearly see that snakes have nostrils. And indeed, they have an olfactory system and can smell with their nostrils, just as we can, but it's the tongue that is the biggest prop.
The snake uses its tongue as part of the system of perception called the vomeronasal system - - because of its relative proximity to the vomer bone at the front of the skull and the nasal system. The vomeronasal system is a sensory organ made up of two small openings in the roof of the mouth in many animals, including humans. This is also referred to as the Jacobson's organ (named for the man who discovered the organ), which for snakes has evolved to be of optimum use for their survival.
The "Smelling" Tongue
When a snake's tongue is flicked out into the air, receptors on the tongue pick up minuscule chemical particles, which are perceived as scent. When the tongue is retracted into its sheath, the tips of the tongue fit neatly into the Jacobson's organ, sending the chemical information that has been gathered through the organ and to the brain, where the information is quickly processed and analyzed so that the snake can act promptly on it.
Why are snakes' tongues forked?
It is believed that the snake's tongue is split so that it knows which direction to move based on the preponderance of chemical particles on one side of its forked tongue in relation to a lesser degree of particles on the other side of the tongue. Think of it as akin to having 3-D glasses for the tongue. The chemical levels are slightly different on the right than the left, but together they make a whole story. This information is subtle, and small animals are fast, so it must be processed as speedily as possible for the snake to catch its dinner.
Or, on the other hand, to prevent the snake from becoming dinner, as it must also analyze information that can detect a predator nearby. And, not least in importance by any means, the tongue, along with the Jacobson's organ, also helps the snake to discover who to take out for dinner, as the chemical receptors in the tongue gather information about potential mates that are nearby.
CAN SNAKES SEE?
Yes, snakes see with their eyes, however their eyesight is not one of their strongest senses. Basically, snakes can see well enough to track pray, but not to discern details and fine movements. Their main sensory organs are the snake tongue and Jacobson's organ. However, some snake species have better eyesight than others, it all depends.