Two tiny openings in the roof of a snake's mouth where it deposits tiny particles it catches on the end of its tongue. It uses this organ as a primary means of smell. Other animals, including lizards, lions, and even people have this organ as well but snakes and lizards use it almost exclusively.

Snakes tongues have forked to adapt to this organ with the tip of each for being placed into one of the openings. You can read more about this organ here