One day, the Gods and the demons, allies for once, struggled to obtain the immortal elixir, tirta amertha. First, they moved the huge Mount Mandara to the sea. Then, the snake, Naga Anantaga, coiled around it, and the Gods and the demons worked together at making it spin like a top, in order to stir up the sea like milk, and extract the elixir of immortality that they all coveted. They collected the elixir in a flask called kamandalu, which the demons stole right away from the Gods. Luckily, Wisnu was more cunning. Disguised as a very pretty girl (demons just love beautiful girls) he managed to easily seduce them. Having fallen under his charm, they immediately entrusted him with the flask. Wisnu ran away with it and brought it back to the other Gods, so that they could dring it down as quickly as possible. But having taken advantage of the confusion, the demon Kala Rauh had already taken an enormous sip of elixir. The sun and the moon immediately denounced him to Wisnu, who cut off his head. But unfortunately, since the elixir had already filled the demon's mouth, his head became immortal.
Since then, Kala Rauh has been relentless chasing the sun and the moon to take revenge. When he catches up with them, he swallows them; but since he doesn't have a body, he's forced to spit them out. This is what causes eclipses, that are luckily just temporary!