I think that Orwell uses specific mental pictures to help develop a larger view of the animals on the farm and their contrasts between one another. I think that one such example would be when Napoleon enters the shed in which Snowball has been constructing elaborate plans for the windmill and simply urinates on them. The image here of Napoleon urinating on something that Snowball has worked on for such a long time brings out his desires to dismiss Snowball and how Snowball's attempts to bring real and lasting change to the farm are futile in the face of Naploeon's power. This contrast is striking in such an image. Another powerful image that brings out contrast between characters would be how Clover looks out for the small ducklings at the moments before Old Major's speech. While the other animals are moving into the barn, thinking only of themselves, Clover is more concerned about the weakest of animals, the ones lost from their mother. While the pigs are sitting right in front, attempting to absorb as much as possible from Old Major's speech, Clover is worried about the most insignificant of animals, perhaps representing Animalism more than Old Major. This is a striking image. Certainly, when Boxer is taken to the Knacker's, Benjamin being the only one to realize what is happening, and being helpless to do anything is another contrasting image that reflects how his own being has been an exercise in futility. The instant when he realizes what is happening to his best friend and he cannot do anything about it is a moment where his own helplessness brought about by his own choice and the helplessness of the other animals brought about their own predicament converge into one powerful image.