In George Orwell’s Animal Farm, the animals on Manor Farm (it’s original name) overthrow Farmer Jones and begin running the farm themselves. The story is an allegory for the Russian Revolution in the early 1900’s. Like the Russians, the animals needed a new system of government to live under. For the Russians it was communism/socialism; for the animals it is animalism.
In the early days of the revolution, as the animals are trying to work out their system, they adopt some key phrases to help them keep their important points in mind. One key phrase is,
Whatever goes upon two legs is an enemy. Whatever goes upon four legs, or has wings, is a friend.”
Initially the chickens were upset at the idea that an animal had to have four legs to be considered a friend, so wings were added as another way of identifying “friends.”