Old Major dies, Animalism is developed by the pigs, the Rebellion happens ahead of schedule, and the Seven Commandments are painted on the barn.
Old Major dies peacefully in his sleep three nights after the meeting. Over the following months, his ideas are taken up by the more intelligent animals, and particularly by the pigs. Napoleon and Snowball are the most active, but a small, fat pig named Squealer joins them. Together, the three develop Old Major's ideas into a coherent system they call Animalism and hold secret meetings to spread it.
The task is not easy. Many animals cannot see why they should rebel against a master who feeds them. Some are loyal to Jones on principle. Moses, the tame raven, distracts animals with his stories about Sugarcandy Mountain, the place where all animals go when they die, where it is always Sunday, and where sugar grows on the hedgerows. Mollie asks whether there will still be sugar after the Rebellion, and whether she will still be able to wear ribbons. Snowball explains patiently that ribbons are a mark of slavery. She is not convinced.
The Rebellion comes much sooner than expected and almost by accident. Jones has been drinking heavily for several days. In June, he goes to Willingdon, gets drunk, and does not return until the next evening, having forgotten to feed the animals. The farmhands hunt rabbits and also fail to feed them. On the following morning, one of the cows breaks down the door of the store-shed. The animals help themselves. When Jones and his men arrive with whips, the animals fight back. Within minutes, the humans are fleeing. Mrs. Jones slips out of a back window with a bag. The gate is shut behind them.
The animals inspect every building and field. They tour the farmhouse, awed by its luxury. They find Mollie playing with Mrs. Jones's ribbons and reprimand her. The farmhouse is agreed to be kept as a museum: no animal shall live there.
Snowball and Napoleon call an assembly. The pigs reveal that over the past months they have taught themselves to read and write using books from the farmhouse. Snowball paints out "Manor Farm" on the gate and writes "Animal Farm" in its place. Then the pigs present the Seven Commandments, which they have formulated from the principles of Animalism and painted on the barn wall. Squealer reads them aloud:
The cows need milking. The animals wonder what should be done with the milk. Napoleon says not to worry about it. When the animals return from the hayfields that evening, the milk is gone.
The Rebellion's accidental nature is one of the chapter's most important details. It is not the result of the organised preparation the pigs have been conducting in secret meetings: it happens because Jones forgot to feed the animals. The revolution Snowball and Napoleon have been planning in theory is triggered by hunger, not ideology. This is historically accurate (the Russian Revolution was precipitated by food shortages and military failure, not by the Bolsheviks' superior organisation) and also significant for what it says about the relationship between ideas and events: the ideology provides the framework but the spark comes from material conditions.
The farmhouse scene establishes something equally important. The animals' agreement that no animal shall live in the farmhouse is the first collective decision of the new state. It will be violated in Chapter 6. Orwell places this agreement here so that the reader registers the original prohibition clearly before it is quietly abandoned.
The disappearance of the milk is the chapter's final image and one of the most efficient anticipations in the novel. Napoleon says "never mind the milk" during the milking scene; that evening it is gone. No explanation is given. The reader is not told who took it. The answer will be revealed in Chapter 3: the pigs have kept it for themselves, and Squealer will explain why this was necessary. But the unexplained disappearance in this chapter begins the pattern: things simply happen, and the official account comes later.
The Seven Commandments are introduced here as a coherent, admirable set of principles. Orwell gives them to the reader in their original, unmodified form so that every subsequent amendment registers against this baseline. The final commandment -- All animals are equal -- will become the novel's central irony when Squealer amends it to read but some animals are more equal than others.