I'd like to point out an interesting aspect of the diary. There are many places in the diary where references to animals are made. For example, in Section 3 the name of the village suffering from a famine is Wolf Club Village. Coincidentally, the villagers ganged up on the "bad" man suspicously like a pack of wolves. The Wolf Club Village in mentioned again in Section 5 when the tenant farmer came into the town from the village, talking about eating a man's heart and liver. Again, in Section 6: Savage as a lion, timid as a rabbit, crafty as a fox, speaking of the Zhao's family dog. In fact, as the story goes on, their are more and more references to animals.
The reference to the dog in Section 6 in a way serves as an epigram to the meaning of the whole story; savage as a lion, timid as a rabbit, crafty as fox. This is the way that the madman perceives his brother along with all of the other people in the town. I think that this was Lu Xun's way of expressing his opinion about pre-revolutionary China. All of these animal references were made from him considering his people like flesh-hungry wolves, in my opinion. He used these animal references along with the cannibalistic aspects to show the effect on the minds of Chinese people at a certain time in their history. Look how crazy it drove the madman to be.