The snake's Jacobson's organ is located in the front of the roof of its mouth where it can be reached by its tongue.
It waves its tongue about in the air and picks up scents that it then transfers into its Jacobson's organ. There the scent is decoded and the organ signals the brain to let it know what the tongue was sensing. Other animals have one but I believe it is the snake that makes the most use of it.
Now, stay away from poisonous snakes and have a great day, you hear?