What is the symbolic meaning of the blurring of the faces of the men and the pigs?

From the text;

"Twelve voices were shouting in anger, and they were all alike. No question, now, what had 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" (97).

This quote clearly symbolizes that there is no longer a difference between the men and the pigs. The animals had gained nothing through their rebellion and had only traded one rule for another.