O Somya, a person has sixteen parts, (and all your sixteen parts are intact). Do not eat anything for fifteen days, but drink as much water as you like. Life is dependent on water. If you do not drink water, you will lose your life.
Śvetaketu did not eat anything for fifteen days. After that he came to his father and said - ‘O Father, what shall I recite?’ His father said, ‘Recite the Ṛk, Yajuḥ, and Sāma mantras.’ Śvetaketu replied - ‘I can’t recall any of them, sir’.
The father said to Śvetaketu - ‘O Somya, from a blazing fire, if there is but a small piece of ember left, the size of a firefly, it cannot bum anything bigger than that. Similarly, O Somya, because only one small part of your sixteen parts remains, you cannot remember the Vedas. Eat something and then you will understand what I am saying’.
Śvetaketu ate something and then went to his father. Whatever his father asked him, he was able to follow.
The father said to him - ‘O Somya, from a blazing fire, if there is but a small piece of ember left, the size of a firefly, the fire can again blaze up when you add some grass. The fire, in fact, can then blaze up even more than it did before’.
‘In the same way, O Somya, of your sixteen parts, only one remained. But that, when nourished by food, has revived, and by that you are now able to follow the Vedas. O Somya, this is why I said that the mind was nourished by food, prāṇa was nourished by water, and speech was nourished by fire.’ Śvetaketu now understood what his father was saying.