Hindu history also contains a story about the churning of the Cosmic Ocean in order to obtain Amrita – the nectar of immortal life. At the suggestion of Vishnu, the devas and asuras churn the primeval ocean in order to obtain Amrita which will guarantee them immortality. To churn the ocean they used the Serpent, Vasuki, for their churning-string. For a churning pole they used Mount Mandara placed on the back of a Great Tortoise – the Kurma Avatar of Vishnu. As the gods and demons churned the sea, the terrible poison Halahala issued from its depths and began to envelop the universe with its choking fumes. Gasping for breath, the devas and asuras sought the help of Shiva, who valiantly took the poison into his throat and swallowed it. Shocked by his heroic act, the Goddess Parvati grasped him by the throat, trapping the poison there and preventing it from spreading; but, such was the strength of the poison, that it turned his neck blue, thereby earning him the name of Neelakanta (blue-throated one). When the Amrita finally emerged along with several other treasures the devas and asuras fought over it. However Vishnu in the form of the enchantress Mohini managed to lure the asuras into handing over to "her" the Amrita, which she then distributes to the devas. Svarbhanu, an asura, disguises himself as a deva and tries to drink some Amrita himself. Surya (the sun-god) and Chandra (the moon-god) alert Vishnu to this deception. Vishnu then decapitates Svarbhanu just as he is about to swallow the nectar, leaving his head and decapitated body immortal. Later the head part is known as Rahu and the beheaded part is known as Ketu.