Chengannur Mahadeva temple is located in the heart of Chengannur town in Alappuzha district, Kerala. There is a popular belief that a divine snake resides in a hole in the western wall of the temple. The temple is also famous for the Goddess worshipped in the temple getting periods(menstruation).
An Azhwar, who was an ardent devotee of Vishnu, challenged a local boy, who was the son of a poison doctor, to prove the greatness of Goddess in the temple and the power of the family over serpents or nagas. The family was famous for curing poison related problems and was an ardent devotee of the Goddess. The family could predict the arrival of poison related incidents and could say which snake had bitten.
That night the boy prayed to the Goddess to prove her presence in the shrine. Goddess appeared in the dream of the boy and told him that in a pipe in her granary a snake was living.
The boy took out the pipe and challenged the Azhwar to make the snake come out of the pipe. Though the Azhwar tried his best he could not.
The boy then commanded the snake to come out. The snake in the pipe came out and started chasing the Azhwar. He pleaded with the boy to control the snake and the boy then requested the snake to go back to the pipe and put the pipe out through the hole in the western wall.
People believe that this divine snake is still there and would bite the one who takes a false oath.
People believe that in the southern part of the temple, several great books with knowledge of poison are buried. It is also believed that if a devotee stands on the rock, under which the books are buried, and meditates on the tip of the sreekovil or sanctum sanctorum, for an entire day, then he would not be affected by poison.