When curd is churned, the finest part of it rises to the surface. That becomes butter.
O Somya, in the same way, the finest part of the food that is eaten rises to the surface and becomes the mind.
O Somya, the finest part of water that is drunk rises to the surface and becomes our prāṇa.
O Somya, the finest part of fire (butter, etc.) that is eaten rises to the surface and becomes our speech.
‘O Somya, the mind is certainly nourished by food, pṛāṇa by water, and speech by fire.’ Śvetaketu then said - ‘Sir, will you please explain this to me again?’ ‘Yes, I will explain again, O Somya,’ replied his father.