The Bhagavata Purana states that Demon Aghasura assumed the form of an enormous serpent. Krishna’s companions, the cowherd boys, entered its mouth, mistaking it for a mountain cavern. After seeing this, Krishna then came to their rescue, killing Demon Aghasura.
The scriptures say that when the boys walked into the cave Krishna became momentarily aggrieved because He knew it was one of Kansa’s tricks. He considered for a moment, and then decided to enter the cave Himself. Demons all over the world became joyful when Krishna went inside. The demigods, who had been hiding among the clouds to see what would happen, became distressed. For a time it seemed as if the snake-demon had killed Krishna, but when Krishna heard the demigods’ pleas He grew larger and choked the demon to death. Demon Aghasura’s life air burst through a hole in his skull and waited there for Krishna to come out, and then it merged into His body. Krishna showed His benevolent nature by rescuing His friends and giving liberation to Demon Aghasura.
Agasura, is a demon (rakshasa) in Hindu and Vedic scriptures.
He was one of Mathura’s King Kamsa’s generals, elder brother of the demoness Putana and Bakasura.
A study of the Bhagavata Purana; or, Esoteric Hinduism by Purnendu Narayana Sinha, p. 247 mentions Agha as one of the tribes in alliance with Kamsa.
The Bhagavata Purana states that Aghasura assumed the form of an enormous serpent. Krishna’s companions, the cowherd boys, entered its mouth, mistaking it for a mountain cavern. After seeing this, Krishna then came to their rescue, killing Aghasura. (The killing of Aghasura by Lord Krishna is narrated by Sage Sukadeva to the king Parikshit in Srimad Bhagavatam).
King Kamsa made many attempts on the life of Krishna, all of them failing. Then he sent Aghasura to kill Krishna, who did so willingly knowing that his younger siblings Putana and Bakasura were killed by Krishna. He assumed the form of the 8-mile-long serpent, disguising his open mouth against a mountain. All the cowherd boys entered the mouth of the demon mistaking it to be a cavern. When the serpent closes his mouth, the people will not be able to breath and eventually, they die.
Krishna entered the serpent upon his arrival and then increased the size of his own body. In response, the demon too extended his own body’s size. Nonetheless, his breathing stopped. Suffocating, his eyes rolled here and there and then popped out. The demon’s life force, however, could not pass through any outlet, and therefore it finally burst out through a hole in the top of Agasura’s head. Thus, the demon meets his end in Krishna’s hand.