How does the last sentence in the book Animal Farm explain the change that has occurred on the farm?

How does the last sentence in the book Animal Farm explain the change that has occurred on the farm?
How does the last sentence in the book Animal Farm explain the change that has occurred on the farm?

LAST SENTENCE: “No question now what has happened to the faces of the pigs. The creatures outside looked from pig to man, and from man to pig, and from pig to man again: but already it was impossible to say which was which.”