Bhashya
वेत्थ यथा अमौ लोकः पितृसंबन्धी- यं प्राप्य पुनरा-वर्तन्ते, बहुभिः प्रयद्भिरपि येन कारणेन न संपूर्यते इति ।न भगव इति प्रत्याह ।वेत्थ यथा येन क्रमेण पञ्चम्यांपञ्चसंख्याकायामाहुतौ हुतायाम् आहुतिनिर्वृत्ता आहुतिसा-धनाश्च आपः पुरुषवचसः पुरुष इत्येवं वचोऽभिधानं यासांहूयमानानां क्रमेण षष्ठाहुतिभूतानां ताः पुरुषवचसः पुरुष-शब्दवाच्या भवन्ति पुरुषाख्यां लभन्त इत्यर्थः ।इत्युक्तोनैव भगव इत्याह ; नैवाहमत्र किंचन जानामीत्यर्थः ॥
In plain words
"Do you know why the other world, the realm of the ancestors where souls go and from which they return, never becomes full, even though countless people die and travel there?" "No, my lord," the boy replied. "Do you know how, at the fifth offering, the subtle waters of the oblation take on a human voice and are called a human being?" Addressed thus, the boy said, "No indeed, my lord." He meant: "I do not understand any of this at all."
Close to the Sanskrit
"Do you know how that world of the ancestors, having reached which they return again, is not filled up even by many departing?" "No, O venerable one," he replied. "Do you know how, by which sequence, in the fifth oblation having been offered, the waters, which are the means and products of the oblation, become called 'man'—that is, they acquire the name 'man' when they are offered and in sequence become the sixth oblation?" Being thus addressed, he said, "No indeed, O venerable one"; the meaning is, "I do not know anything of this at all."