What event sparked the animals' rebellion in Animal Farm?
Old Major's speech put the idea of rebellion in the animals' minds, but they didn't have any idea when it would begin or whether "it would be within their own lifetime." Snowball and Napoleon took to organizing the others, so the animals were ready when the time came. Then, on Midsummer's Eve (in June), Mr. Jones got so drunk that he didn't come home until the next day. After arriving, he went right to sleep without feeding the animals. One of the cows broke down the door to the shed, so Jones' workers began "lashing out in all directions" with their whips. In one sudden, unified rush, the animals attacked the men, who were "butted and kicked from all sides." Mrs. Jones grabbed a few items and ran from the house, joining her husband and the workers in the road, where the animals left them, slamming the gate behind them.
The speech that was given by Old Major triggered all the animals into believing that they had to fight for their right. Old Major's speech was persuasive, followed by the tune Beasts of England, which made the animals feel the need to break free from being under the rule of the humans.
This event, though a small part of the book, was the most important event that started the whole story. In the end, it was definitely not worth it, as the pigs were influenced by the humans and took control of all the animals.