A day dedicated to the snake god better known as Nag Devta. On this day the Hindu’s offer milk to the Nag devta (cobra) who is sacred to all Hindu’s with his omnipresence, wrapped around Lord Shiva’s neck. I don’t think anyone has seen a Lord Shiva statue or picture without a cobra all hooded in full glory.
The Hindu’s believe that it is very auspicious to have a darshan of a Nag devta on this day. Snakes have been revered by the Hindus since time immemorial. There are many snake god temples in India.