The Churning of the Ocean of Milk (Khmer: Ko Samut Teuk Dos, also called samudra manthana in Hindi) is one of the best-known episodes in the Hindu philosophy narrated in the Bhagavata Purana, in the Mahabharata and in the VishnuPurana.
The Churning of the Ocean of Milk explains the origin of amrita, the nectar of immortality.
It is said that a long time ago, Devas (Gods) and Asuras (Demons) were fighting against each other to ensure their domination over the world. After many years of war, the Devas were defeated and the Asuras, led by Valin, gained control over the universe. The Devas sought Vishnu's help, who advised them to treat the Asuras in a diplomatic manner. The Devas formed an alliance with the Asuras to jointly churn the ocean for the nectar of immortality and to share it among themselves.
The Churning of the Ocean of Milk was an elaborate process: Mount Mandara was used as the churning rod, and Vasuki, a naga who abides on Shiva's neck, became the churning rope.
Vishnu knew that Vasuki would vomit poisonous flames when twisted and pulled, and therefore advised the Devas to hold the tail end of the snake, without telling them the reason. First, the Devas held the head end of the snake, while the Asuras held the tail end. The Asuras were enraged by this, as the lower part of an animal is less pure than the part that contains the head. They insisted on holding the head side of the snake. Vishnu had an inkling that his reverse psychology would work.
The Asuras demanded to hold the head of the snake, while the Devas, taking advice from Vishnu, agreed to hold its tail. When the mountain was placed in the ocean, it began to sink. Vishnu, in the form of Kurma, came to their rescue and supported the mountain on his shell. The Asuras were poisoned by fumes emitted by Vasuki. Despite this, the Devas and the Asuras pulled back and forth on the snake's body alternately, causing the mountain to rotate, which in turn churned the ocean.
The demons were weakened, after a thousand years of efforts, by the naga’s poison. The Devas eventually took the amrita, and from this moment, the Devas would rule the world and send the Asuras to hell.
Many treasures came out of the Ocean of Milk. Amongst them were celestial creatures called Apsaras coming on earth to entertain gods and kings.