This is a great question. There is also a good answer for this. Here is some of the background that might be helpful. The book was published in August 1945. This is still the context of World War II. Also there was a rising feeling among the British and Americans that Stalin was a force that they needed to oppose. Orwell did not like what he was seeing. Although he was democratic socialist, he was very wary of Stalin. He did not agree with his type of communism with all the abuses of power - the arrests, which seemed arbitrary, censorship, and simple abuse of power.
So, what's this bloody pile of corpses doing in the middle of Orwell's "Fairy Tale"? The whole episode alludes to the 1930s Great Purge, . the Great Terror (we'll say). During the Great Purge, Stalin cleaned house. Thoroughly. Some people just disappeared; others were sent to the Gulag prison camps ; others had to confess publicly to crimes they'd never committed. Officially, he was getting rid of "counter-revolutionaries"; unofficially, he was getting rid of anyone who disagreed with him. (Check out "Symbols, Imagery, Allegory" for more details on the hen rebellion and Stalin's purges.)