A snake may appear threatening when it flicks its tongue out, but it's simply trying to get a better sense of its surroundings by "tasting" the air.
To compensate for their poor eyesight and limited hearing , most snakes have an excellent sense of smell. Although snakes have nostrils, they also use their tongues to pick up the scent of nearby prey or predators.
When a snake flicks its tongue, it collects odors that are present in miniscule moisture particles floating through the air. The snake darts the tongue into its Jacobson's organ, which is located inside the roof of the snake's mouth.
The prongs of the forked tongue fit perfectly into the two holes in the Jacobson's organ, which is also known as the vomeronasal organ. After the tongue transfers the moisture-borne scent particles into the vomeronasal organ's opening, some of the chemical compounds they contain bind to the organ's receptor molecules.These receptors send sensory messages to the reptile's brain , which interprets the sensory information as a smell, such as the scent of a mouse.
While the moisture-borne odor particles are detected through Jacobson's organ, air-borne scent particles are analyzed through the snake's nasal chamber, which also contains sensory cells that interpret smells.
The Jacobson's organ is also found in a few lizard species, including chameleons and iguanas.
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