The image on his retina just does not go into him.

His unconsciousness is filled with a strong, dark, vague prescience of a powerful presence, a two-eyed, four-legged, long-maned presence looming imminent.
And to _force_ the boy to see a correct one-eyed horse-profile is just like pasting a placard in front of his vision.

It simply kills his inward seeing.

We don't _want_ him to see a proper horse.

The child is _not_ a little camera.