In Chapter 7, the hens stage a bit of a mutiny. Napoleon has told them that their eggs are going to be taken and sold because the farm needs to buy food to survive. The problem is that Animalism is against selling things like eggs.
Because of this, the hens start smashing their eggs so they can't be sold. Napoleon then starves a bunch of them to death. He says that anyone who gives them food dies. He lets nine of them die and then the rest fall in line and do what he says.