Once upon a time, as now, mother earth was overburdened with the weight of millions of arrogant kings. Assuming the form of a cow, her face overflowing with tears, she approached Brahma, the god of creation for protection.
Realizing her piteous condition, Brahma, accompanied by the earth and all the other gods, went to the ocean of milk, the abode of the Supreme Lord Narayana. There, Brahma venerated the Lord by chanting the Purusha Sukta from the Rig-Veda.
While he was thus contemplating, Brahma heard a voice in the sky: “God already knows the affliction of the earth. He will manifest Himself as Krishna and reduce the burden of the earth.”
Hence, saving the earth from the clutches of evil kings was the part motive for Krishna’s birth. Another primary reason was to give blissful joy to the simple cowherds of Vrindavan, their women, and cows. In Vrindavan, Krishna behaved much as a normal child of His age would do. He teased the gopis, respected His elders and also picnicked with His friends.
No sooner had Krishna also walked in following His friends, than the serpent closed his mouth. Caught inside, Krishna expanded Himself within the throat of the demon. Soon, the demon was choking and struggling for breath.
His prana, restricted within the body, finally burst out through his skull (brahmarandhra), and a bright and strange light illuminating the directions emerged from him, and waited in the sky. As soon as Krishna came out of the serpent’s body, the light merged into Him. Now, this is the kind of end only high-class yogis achieve. The Taittriya Upanishad describes this.