How does Iain Banks use imagery in The Wasp Factory: A Novel?

Imagery:

"After I'd come to understand evolution and know a little about history and farming, I saw that the thick white animals I laughed at for following each other around and getting caught in bushes were the product of generations of farms as much as generations of sheep; we made them, we moulded them from the wild, smart survivors that were their ancestors to that they would become docile, frightened, stupid, tasty wool-producers. We didn't want them to be smart, and to some extent their aggression and their intelligence went together. Of course, the rams are brighter, but even they are demeaned by the idiotic females they have to associate with and inseminate."