तेजसः सोम्याश्यमानस्य योऽणिमा स उर्ध्वः समुदीषति सा वाग्भवति ॥ ६.६.४ ॥
In plain words
Of heat that is consumed, my dear, the finest part rises upward and becomes speech.
The commentators
Chāndogyopaniṣadbhāṣyam· bhāṣya
एवमेव खलु सोम्य तेजसोऽश्यमानस्य योऽणिमा स ऊर्ध्वः समुदीषति सा वाग्भवति ॥
In plain words
In this very way, O gentle one, of the fiery food that is consumed, whatever subtle essence rises upward becomes speech.
Close to the Sanskrit
Even so indeed, O gentle one, of fire being eaten, whichever subtle essence rises upward, that becomes speech.