Anna Sewell wrote the mood in the novel Black Beauty to be sad and for the reader to feel compassion for the horses. When the horses get abused.
Anna Sewell try to express the idea of the pain and suffering of animals was done through human feeling towards the story.
Anna Sewell has to convey every person to abuse animals because of the fact that animals are sentient beings with minds. Pain is the same simply can not be expressed in words.