“And the gods and the Asuras made Mandara churning staff and Vasuki the cord, and set about churning the deep for amrita. The Asuras held Vasuki by the hood and the gods held him by the tail. And Ananta, who was on the side of the gods, at intervals raised the snake’s hood and suddenly lowered it. And in consequence of the stretch Vasuki received at the hands of the gods and the Asuras, black vapours with flames issued from his mouth.

In plain words: The gods and Asuras used Mount Mandara as the churning stick and the great snake Vasuki as the rope. The Asuras held his head and the gods held his tail. As they pulled him back and forth, smoke and flames came out of Vasuki's mouth.