Here is the detail of a man carrying the bale from Homer's final drawing as it was published. If the image of the head of the horse is fixed in your mind, you might be able to imagine that you are seeing it here as this man's abdomen. If you see the man's abdomen as a horse head, that is an illusion*, in the context of the painting. You are seeing it not as what it is, but as something it is not. The horse head, the illusion, in turn, functions as an allusion, suggesting the idea that the man is functioning as a pack horse. Like Vedder's Valentine cards with the extra ideas in the poems, this was probably also missed by the publisher.
This distortion is not as obvious as the example of the mother/child in the Boat Builders. The real and ideal are better balanced here. Although, compared with the drawings, the abdomen is less realistic in order to concurrently represent the horse head, it seems to remain sufficiently true to Nature. At the same time, the image of the horse is not so distinct, which also makes it harder to prove intention. We have already discussed how the image of the horse can be an allusion, suggesting the idea that the man is like a pack horse. Because that provides a motive, the functional relationship of the horse head image in the picture helps to support the idea that this is something Homer actually intended.
* Note: Visual artworks, of course, are all about illusion. In these discussions, I will be referring to objects in the scene, in the real context represented, as being what the thing actually is. Objects that are not real in the context of the artwork, "what the thing is not," will be considered illusions. Any object in the work, real or illusion, can provide an allusion, suggesting the idea of something else.