One of the promises of the new order that was ushered in after the Rebellion, when the animals could run their own affairs, was that hens would be able to hatch more of their eggs. Old Major says at the beginning of the book:
And you hens, how many eggs have you laid in this last year, and how many of those eggs ever hatched into chickens? The rest have all gone to market to bring in money for Jones and his men. And you, Clover, where are those four foals you bore, who should have been the support and pleasure of your old age? Each was sold at a year old — you will never see one of them again.
Later, when the hens learn that Napoleon has signed a contract to sell 400 of their eggs a week, the hens first raise a "terrible outcry." They have been sitting on their eggs with the idea of hatching them, and they call taking the eggs "murder." They mount something akin to a rebellion by refusing to cooperate. They lay their eggs on high rafters, where they roll to the ground and smash. Napoleon retaliates by cutting off the hens' food supply and threatening death to any animal giving the hens as much as one piece of grain. Eventually, after five days, and the death of nine hens, the surviving birds capitulate and begin laying their eggs in their boxes again.
The hens, rather than allow their eggs to be sold by Napoleon and his henchmen in chapter 7, lay their eggs on the rafters so that the eggs will smash on the floor of the barn. They consider what Napoleon wants to do to be murder. Because Napoleon and Whymper have agreed to sell 400 eggs a week, they punish the hens by not giving them any food. The hens hold out for five days and then they give in, allowing Whymper to collect the 400 eggs a week.