First of all, this statement alludes to the fact that they're trying to say that animals are good, and humans are bad- because that's the main idea in most parts of the book. The animals have risen up and created their own rules for the farm in the wake of the human oppression previously not occurring and brought to life by the speech of Old Major. There are two main problems:
First of all, the whole farm runs on animals - however, pigs remain sovereign. The problem is, although most animals do have four legs, some animals, like swans, birds, and chickens, don't. That means they're left out and perhaps their contribution to the farm can be lost as a result of the fact that their physical anatomy betrays the ideals of the Commandments.
Secondly, we discussed before how this leaves out humans. However, they need humans- especially for the windmill at the beginning. If you remember, Napoleon actually had to make deals with some, and those proved to be very beneficial. This pretty much means that Napoleon is trying to dictate the beliefs of the beings he rules, but breaks and bends his own rules when he wants. After all, he became the leader after a revolution on the farm and uses his attack dogs in place of military force. Sound familiar? Napoleon represents Joseph Stalin, and most other characters represent people from history. One of the main points of this book is looking at it from another perspective. The animals mean something, it's more a book about the actions of people.
