My image

There is a part in this book which is when Snowball is giving a speech to his comrades about the construction of a windmill.

Well, Napoleon, has I understand was jealous of his creation and was worried about the increasing of popularity that Snowball had had in the last days, first with the tactic that gave them the victory against Mr Jones and now with this appealing project.

So given this facts he planned one attack against is rival and it consisted in realising the dogs he had raised against Snowball and make him go away.

And that his what this image symbolizes, if you think that the pig is Napoleon with book about the construction of the windmill giving the order to his dogs to attack Snowball that is in the barn among the other animals.