Watching Lord Krishna’s closeness to the cowherd boys, Brahma was jealous. He could not digest the fact that the Lord was allowing the boys to take liberties with Him, in the name of friendship. So Brahma stole all the cows that the boys were grazing, and not content with this, he took the boys away too.
Krishna, aware of what Brahma had done, decided to teach him a lesson. He took the form of every cow that had been stolen, every calf that had been stolen, and the form of every boy who had disappeared.
He also became every rope used to tether the cows, every stick used to herd them. He became the vessels in which the boys had brought food, and the Antaryami in every form He took.
Thus when the crowd of boys went back to Gokula, not one was missing, for Krishna had taken the form of every one of them. Not one cow was missing either. But Balarama noticed that the cows and the boys now had effulgence that they had lacked earlier. For one year, Krishna kept up this act of His, elaborated Kidambi Narayanan, in a discourse. Brahma was taken aback at what he saw. All the boys and cows he had taken away were all in Brahmaloka, and yet all of them were in Gokula too, on the banks of the Yamuna! So which was real, and which was false?
An agitated Brahma went back to Brahmaloka, to have another look, and there another shock awaited him. Seated there was his own image, and this replica of his asked him who he was! Brahma ran to have another look at Gokula. There one minute he saw Krishna, the next he saw cows, and the next minute he saw the Yadava boys. Realising his folly, Brahma came to Krishna and begged His forgiveness.
This leela of Krishna’s is as amazing as His eating a fistful of mud.
On that occasion, Yasoda saw inside His mouth all the worlds. She also saw a Krishna inside His mouth, and this Krishna too had His mouth open, and inside His mouth too she saw the same scenes replicating themselves infinitely.
As amazing as this was the Brahma Mohanam, so called because it left Brahma confused and finally humbled.