Kalakootam is the name of a poison created from the sea when Devas (Gods) and Asuras (Demons) churned it (Samudra manthan) in order to obtain Amrita, the nectar of immortality.

Kalakootam is the name of a poison created from the sea when Devas (Gods) and Asuras (Demons) churned it (Samudra manthan) in order to obtain Amrita, the nectar of immortality.

Fourteen different ratnas (gems) were recovered in this exercise, mostly retained by the Gods after the Demons tried to cheat them. But before Amrita could be recovered, Kalakootam/Halāhala ("the most vicious and venomous poison of universe") was produced, which started killing both sides. As no one could bear the poisonous fumes emitted by the poison, both Devas and Asuras began to collapse due to asphyxiation. They ran for help to Brahma, who looked to Vishnu for advice. Vishnu said that only Shiva could digest the deadly poison. So both parties went to Kailasha and prayed to Lord Shiva for help. Shiva chose to consume the poison and thus drank it. His wife Parvati, alarmed, stopped it in his throat with her hands, thus earning him the name Viṣakaṇṭha (the one who held poison in his throat). He was later saved by the mahavidya (tara) who is also a form of parvati. The poison made his throat turn blue; hence, he is also known as Nīlakaṇṭha (the one with a blue throat).

courtesy: Wikipedia