The answer is: The animals are endowed with human characteristics and motivations.
A fable is a story in which animals are represented as possessing human characteristics and qualities in order to express a point of view, usually of a moral nature. In Animal Farm, Orwell depicts the events that led to the Russian Revolution of 1917 and then to Stalinism by making use of certain animal characters. Orwell was a harsh critic of any kind of authoritarianism, which, under Stalin, he believed Russia had fallen under this category.