Mark Twain is a brilliant author if we think about anthropomorphism.
The whole story is told by a dog and I suppose that the main reason using this tool in his work was to sensitize people about cruel behavior towards the animals. Anthropomorphism was broadly used in Middle Ages literature, nowadays it is a very common device used in children literature. It helps the author appeal the interest of a reader and makes it special.So why people think that they have rights to domain another species, hurting them and raise them for later to put their flesh on a plate, to entertain themselves or test new medicine on it. Human cruelty is a real thing and its roots lay centuries back in history.