The Four Nutriments: what do the metaphors in SN 12.63 mean? In the Puttamansa Sutta, the Four Nutriments ('ahara') of physical food, sense contact, intention &amp; consciousness are discussed using four comparative similes ('metaphors'). 

The 1st simile of eating the flesh of one's own son (merely for the sake of crossing the desert) is very straightforward. However, the remaining three similes of a 'skinned cow', of 'two strong men dragging a man into a pit of fire' &amp; of a 'thief punished by a king' are not obvious in their meaning. 

These three similes are: 


  And how, O monks, should the nutriment sense-impression be considered? Suppose, O monks, there is a skinned cow that stands close
  to a wall, then the creatures living in the wall will nibble at the
  cow; and if the skinned cow stands near a tree, then the creatures
  living in the tree will nibble at it; if it stands in the water, the
  creatures living in the water will nibble at it; if it stands in the
  open air, the creatures living in the air will nibble at it. Wherever
  that skinned cow stands, the creatures living there will nibble at
  it.
  
  And how, O monks, should the nutriment volitional thought be considered? Suppose, O monks, there is a pit of glowing embers, filled
  to cover a man's height, with embers glowing without flames and smoke.
  Now a man comes that way, who loves life and does not wish to die, who
  wishes for happiness and detests suffering. Then two strong men would
  seize both his arms and drag him to the pit of glowing embers. Then, O
  monks, far away from it would recoil that man's will, far away from it
  his longing, far away his inclination. And why? Because the man knows:
  'If I fall into that pit of glowing embers, I shall meet death or
  deadly pain.'
  
  And how, O monks, should the nutriment consciousness be considered? Suppose, O monks, people have seized a criminal, a robber, and brought
  him before the king saying: 'This is a criminal, a robber, O Majesty!
  Mete out to him the punishment you think fit!' Then the king would
  tell them: 'Go, and in the morning strike this man with a hundred
  spears!' And they strike him in the morning with a hundred spears. At
  noon the king would ask his men: 'How is that man?' — 'He is still
  alive, Your Majesty.' — 'Then go and strike him again at noontime with
  a hundred spears!' So they did, and in the evening the king asks them
  again: 'How is that man?' — 'He is still alive.' — 'Then go and in the
  evening strike him again with a hundred spears!' And so they did.


What do we think each of these similes means?
The Four Nutriments ('ahara') of physical food, sense contact, intention &amp; consciousness are true for the worldlings who have craving (tanha) and greed (lobha) or aversion / revulsion (dosa), caused by ignorance (moha).  Tanha, lobha, dosa, moha provides nourishment for the continuation of life from existence to existence. 

The worldlings have  five aggregates of clinging (Panca Upadana Khandas).  In the case of Arahants – the awakened ones - there is no craving. They have rooted out the “I concept”.  They have fully realized five groups of existence and the five grasping groups of existence (Panncakkhandha and panca upadanakkhandha) .  Arahants have only the five aggregates in detachment  (Anupadana).  Upadana means ‘grasping’ and Anupadana means ‘non-grasping’ or letting go.While Upadana leads to Samsara, Anupadana leads to Nibbana.

To put it in another way, (for better understanding), after the elimination of all defilements an arahant lives in society without Upadana or Attachment to any thing in the world. He does not have the five grasping groups (pancaupadanakkhandha) but only five groups,aggregates (Pancakkhandha), namely, rupa (body), vedana (feeling), sanna (perception), sankhara (volitional formation), and vinnana (consciousness).  His consciousness is ‘translucent’ (for wont of a better word) as no food is provided. In this he is immeasurable - is like the Buddha. All measurement is from a here to a there, with in-betweens. In the Buddha, there is neither a here nor a there nor any in-between. He is thus immeasurable. See Bahiya Sutta: About Bahiya - Ud 1.10


  “Then, Bahiya, you should train yourself thus: In reference to the seen, there will be only the seen. In reference to the heard, only the heard. In reference to the sensed, only the sensed. In reference to the cognized, only the cognized. That is how you should train yourself. When for you there will be only the seen in reference to the seen, only the heard in reference to the heard, only the sensed in reference to the sensed, only the cognized in reference to the cognized, then, Bahiya, there’s no you in that. When there’s no you in that, there’s no you there. When there’s no you there, you are neither here nor yonder nor between the two. This, just this, is the end of stress.” (Ud I.l0)...


An arahant is sustained by ONLY the physical food that does not create upadana. He does not have the other three ‘mental’ foods as he has rooted out the “I concept”.  He is free from attavada upadana by seeing it as a deceit (the true nature). So if there is no nutriment  consciousness, an Arahants  consciousness is mere presence.  Since there cannot be presence without something being present, it is what distinguishes living from non-living, such as tables and chairs. The Buddha has stated that consciousness is dependently arisen, since without a condition there is no origination of consciousness. In an Arahant, Paticcasamuppada (dependent arising) ceases.  Which means Vinnana paccaya (conditioned by consciousness) too ceases.