Orwell's fourth chapter is a look into the outside world. This is really more or less a reality check after so much narrative about the utopian lifestyle of Animal Farm. The passage does clear up a few questions any inquisitive reader would have about the outside world. I mean, wouldn't you think that the other neighboring farmers might think something's up if one day they see a bunch of pigs supervising horses plow a field? Anyway, Orwell explains, "It was lucky that the owners of the two farms which adjoined Animal Farm were on permanently bad terms." Anyone considering the allegorical significance of Foxwood and Pinchfield might guess that they are really just deep metaphors for the nations bordering Russia. (More on this in the metaphor profile section--click on side links.)
Anyway, these farmers just shrug off the animal rule as a gimmick and don't think much of it until they realized that the animals are actually being more productive than Jones had been. They also get a little nervous when they realize that the Animal Farm pigeons have gone to neighboring farms, teaching other animals the "Beasts of England" song and encouraging them to revolt. So the farmers next strategy is to criticize the farm, saying that the animals "practiced cannibalism, tortured one another with red-hot horseshoes, and had their females in common." This symbolizes the outcry of America and other Western nations during the beginning stages of the cold war. Ridicule was really the only tactic they had left after being scared to death of the Soviet powers after World War II.
The real action in the chapter is when Jones and his men try to recapture the farm. Napoleon and his pig allies had long expected this to happen, so they plan a very extensive defense strategy. When the Jones crew attacks, "they were gored, kicked, bitten, and trampled on." So many of the men die, thus concluding the Battle of the Cowshed.
The final metaphor is the reference to the shotgun of Mr. Jones. Really this part of the allegory is pretty neat. The pigs decide to prop the gun up, pointing it toward the gate from which Mr. Jones and his men attacked. In Russian terms, the gun may represent the Soviet decision to begin making nuclear weapons to later use on the United States.