As the Shatapatha Brahmana tells it
Shatapatha Brahmana 14.1.1 · 3 min read
The gods once sat down together for a long sacrifice. Agni was there, and Indra, Soma, Makha and Vishnu, and all the other gods except the two Ashvins. The place they chose was Kurukshetra. People still call that plain the gods' own place of worship.
They had come with a wish.
"May we become excellent," they said. "May we become glorious. May we never lack food."
Then they made an agreement among themselves.
"Whichever of us reaches the end of the sacrifice first," they said, "by effort, by faith and by offerings, he shall be the best of us. And what he wins shall belong to all of us in common."
"So be it," they all said.
Vishnu reached it first. He became the most excellent of the gods, and that is why people say, the old book notes, that Vishnu is the best of the gods.
But he had agreed to share, and now he found that he could not. The glory was his and he wanted to keep it. The book does not blame him much. Even now, it says, not everyone can master his own love of glory.
Vishnu took up his bow and three arrows and stepped away from the others. He stood there with the bow planted on the ground and his head resting on its upper end.
The gods wanted what he had won. They did not dare to attack him. So they sat down in a ring all around him and waited, and nothing happened.
Then the ants spoke up. They were the small kind that are said to find water wherever they dig.
"What would you give," the ants asked, "to someone who gnawed through that bowstring?"
"We would give him food to enjoy for ever," said the gods. "And he would find water even in the desert."
"So be it," said the ants.
They crept up to the bow and began to gnaw. The string parted. The two ends of the bow sprang apart, and they cut off Vishnu's head.
The head fell with a sound, and the book gives the sound. It was "ghrin". As it fell it became the sun we see in the sky. The body lay stretched out on the ground, pointing east.
"Our great hero has fallen," said the gods.
They ran to him, each one eager to be first. Indra got there before the rest. He pressed himself against the fallen body, limb to limb, and took it wholly into himself, and in doing so he became the owner of that glory. This, says the book, is the secret of one of Indra's names. Makha is another name for Vishnu the sacrifice, so Indra became Makhavat, and people say Maghavan.
The gods kept their promise to the ants. Then they divided the fallen sacrifice into three parts, for the morning, the midday and the evening offerings, and went on worshipping with it.
It was a sacrifice without a head. Only one sage, Dadhyanch, knew how the head could be put back, and Indra had forbidden him to tell. But that is another story.
As the Devi Bhagavata Purana tells it: the horse's head
Devi Bhagavata Purana, Book 1, chapter 5 · 2 min read
The Devi Bhagavata Purana tells of the bow and the ants again, and almost nothing else is the same.
Vishnu had fought a war for ten thousand years, and he was worn out. He sat down on level ground, set his strung bow upright, rested his head on the end of it and fell fast asleep.
The gods were beginning a sacrifice, and they needed him. Indra, Brahma and Shiva found him sleeping.
"How do we wake him?" Indra asked.
"If we break his sleep he will be angry," said Shiva. "But the sacrifice must be finished."
Brahma made a white ant and told it to eat through the end of the bow that rested on the ground, so that the bow would jerk and wake the sleeper.
The ant was not willing. "To wake someone from deep sleep is a sin," it said. "And what do I gain by it?"
"Whatever butter falls outside the fire pit at a sacrifice shall be yours," said Brahma.
So the ant gnawed. The string gave way, the bow sprang up with a terrible noise, and the earth shook. When the dark cleared, Vishnu's body sat there without its head. Nobody knew where the head had gone.
The gods wept. Then, on Brahma's advice, they prayed to the great Goddess, and a voice answered them from the sky.
"Nothing happens without a cause," the Goddess said. "Vishnu once laughed while he was looking at Lakshmi's face. She thought he was laughing at her, and in her anger she said, let your head fall off. There is a second cause. A demon named Hayagriva, the horse-necked, has my promise that only one with a horse's face can kill him. Let a horse's head be fixed on Vishnu's body."
The gods' craftsman cut off the head of a horse and set it on Vishnu's shoulders. Vishnu rose as Hayagriva, and he killed the demon.