The line "The pigs are walking!" uttered by Dr. Arzt is a reference to George Orwell's Animal Farm. When the animals took control of the farm, all of the animals were supposed to be equal. The pigs quickly took over and began to adopt human mannerisms. The more corrupt and in control they became, the more like humans they became. When they started to walk it was a sign that there was a definite controlling group in place, similar to the way things were on the island.