In what Sutta(s) is there a References to Imagine the Body Inside Out and What is Below the Skin
Could it be the Puttamansa Sutta: A Son's Flesh SN 12.63 that you are seeking?
In this Sutta, Buddha speaks of four kinds of nutriment: edible food, sense-impressions, volitions, and consciousness. Under Sense-impression there is this simile of a skinned cow that points out that wherever she stands, will be ceaselessly attacked by the insects and other creatures living in the vicinity.

&quot;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.
&quot;In that manner, I say, O monks, should the nutriment sense-impression be considered. If the nutriment sense-impression is comprehended, the three kinds of feeling are thereby comprehended. And if the three kinds of feeling are comprehended, there is, I say, no further work left to do for the noble disciple.

Like a skinned cow, man is helplessly exposed to the constant excitation and irritation of the sense-impressions, crowding upon him from all sides, through all six senses.