In time his teacher came back, and said to him: 'Upakosala.' He answered: 'Sir.' The teacher said: 'Friend, your face shines like that of one who knows Brahman. Who has taught you?' 'Who should teach me, Sir?' he said. He denies, as it were. And he said (pointing) to the fires: 'Are these fires other than fires?' The teacher said: 'What, my friend, have these fires told you?'

In plain words: When Satyakama returns, he sees Upakosala's face glowing like one who knows Brahman and asks who taught him. Upakosala hints shyly that the fires did, and the teacher asks what they said.