Chapter 7 is really one of the low points for the animals of Animal Farm. As you mentioned, they have to work really hard trying to build the windmill. But there are other things going on as well.
- The winter is a really hard one -- terrible weather.
- They did not have enough food. Their corn ration was cut back and the potatoes that were supposed to make up for that spoiled.
- The other thing that I see as a hardship is all the executions and the fact that Napoleon is forcing the hens to allow their eggs to be sold.
Starvation: The cornration was drastically reduced. There was terrible weather and not enough food to survive.