One day, Krishna planned a picnic near Nandanvan. So rising early in the morning, He awakened his fellow cowherds sounding a horn. Together, all the cowherds, and their cattles went to the forest. There, on the bank of Yamuna river they began to play joyfully.
Nandanvana was in fact an abode of the demon Aghasur. He was sent there by Kansa. Seeing the boys playing, he felt extremely jealous. Knowing that Krishna had killed his brothers Bakasur and sister Pootana. It seemed an ideal moment for the demon to avenge the death of his siblings. Thinking thus, the demon took guise of python and lay in the way and opening his mouth like an opening of a cave. The cowherds too fell in his trap. Thus driven by curiosity, all the cowherds entered the demon mouth one by one. When Lord Krishna saw that his friends had entered demon’s mouth. He too entered it to protect them. Aghasur wanted to masticate the cowherds including lord Krishna; but the lord increased his body and choked demon throat. Now the breath of demon stopped. His eyes rolled over and at last his life left his body through Brahmrandhra (cosmic pore). With his ambrosial eye, Lord resurrected these dead fellows and their cattles and together they came out of the demon’s mouth. As soon as the demon died, a divine flame emerged from the python’s mouth. It waited there sometime for God. And when lord Krishna came out, the flame mingled with him.