After constant fighting with Asuras, Devas were tired and wanted to attain immortality. They went to Vishnu, who instructed them to churn the big milk ocean (parkadal) which will yield the sweet Nectar (Amrith).
We say there are 330 million devas (33 crores). Vedas show us 33 devas in total (11 rudras, 12 adityas, 8 vasus, Indra and Prajapati) with a crore of incarnations of each.
The devas and asuras stuck a deal and set out to get the nectar. Vishnu took the form of a huge tortoise (Koorma Avatar) holding the Matragiri mountain and stabilized it. The snake Vasuki became the rope and they churned the ocean. The devas were clever and gave the head side of the snake to asuras and they took the tail end. With constant back and forth, the snake got agitated and started to spit poison. At the same time, a dangerous poison came out of the ocean – both combined called Hala-Hala (Hala-poison). Vishnu wanted to help, and as he got closer, the heat from the poison turned him black.
Not knowing what to do, they went to Kailash to seek Siva’s help. After getting permission from Nandhi, they met Siva and ask for his help in dealing with the poison.
Side story: Nandhi Deva is one blessed with Siva Swaroobam. Once Ravana was flying his chariot over tha kailash and he was stuck. Nandhi instructed him to go around as Siva is resting. Ravana replied, You look like a monkey and how can you stop me? Nandhi cursed, your city will be destroyed by a monkey. A thousand hanumans cannot destroy Lanka without this curse. It was Nandhi’s curse that helped Hanuman lit fire of Ravana’s lanka]].
It is customary to give the first harvest or first produce to the god. [Even now, some deposit their first month salary in a hundi]. Devas said, they were there to give the first product from the ocean churning to Siva as it is the custom. What they were saying is true, but what are they giving him? A potent and dangerous poison.
The ever compassionate Siva, smilingly asked to bring the Hala Hala poison; then rolled it in to a ball and took it like candy in one swoop. If the poison goes inside, the entire universe will be doomed. If it is outside, all these devas and asuras are doomed. Siva has a selfish reason too to take the poison. Without all the devas their wives will become widows and will cause more chaos. Wearing white sarees, everyone will look like kalaivani (goddess saraswathi) and no sumangali will be left to take aarthi even for parvathi.
He kept it in his throat without swallowing or spitting it out. [[Others point out Parvathi concerned about Universe put her hands around Siva’s neck and stopped the poison from moving further]]. When the poison lodged in his throat, his neck become blue, hence he called Neelakandan (blue-neck).
Siva resting on Parvati’s lap as she puts her hands around his neck to stop the poison from moving further– Suruttapalli Pallikondeshwarar temple- Andra Pradesh
He is also referred as Sugreevan – beautiful neck (greevam – neck), Murugan called Sathgreevan (six neck), Ravana called Dasa grevean – 10 heads/necks.
The devas relieved, went back to the churning. Out of the ocean, many great things came. Kamadhenu (cow) – which gives what you ask for, karpaga tree – which gives what you think, parimala, chintamani, mandagini, choodamani and many – everyone took their shares. Last came the sweet nectar (Amirtham). Vishu took jagan mohini form, cheated fellow asuras who helped to churn, and gave it to devas only.
The day Amrith appeared is Ekadasi (Auspicious day for Vainavites). The next day, on Dwadasi, the devas are celebrating and were joyful having attained immortality and forgot about thanking Lord Siva. If i dropped my pencil and someone pick and give it back, i would say thank you. If i say thank you to the person who gave my own pencil, don’t you think the great Siva should be thanked too for taking the poison.
Finally they realized the blunder – if he hadn’t taken the poison, we would have died that day. They took bath in Ganga and headed over to kailash to worship siva and perform Pooja [[Meaning: (poo – poorthi /completion, ja – creation) – to complete (end) the maya/karma in our mind and to create siva jynana (liberation)]].
They cried and prayed to him for forgiveness. The ever compassionate lord forgave them and performed his Rudra dance. With the celestials playing music and singing, Siva danced between the horns of Nandhi devar. This is called Anantha Thandavam (Happy Dance). Arunagiri explains this dance well in his poem: The Chandra (moon on siva’s head) also moves, Nandhi playing mathala (drums), Siva playing Udukai, Saraswathi playing veena and the position of his hair which was normally bent when tied up.