What is the inciting incident in the novel Animal Farm?

The first chapter shows Old Major giving his speech to the animals. He is inspiring and convinces them that man is the reason that the animals have such terrible lives. He ends his speech with the song "Beasts of England." With this, the animals are quite fired up and inspired. 

And then, after a few preliminary tries, the whole farm burst out into Beasts of England in tremendous unison. The cows lowed it, the dogs whined it, the sheep bleated it, the horses whinnied it, the ducks quacked it. They were so delighted with the song that they sang it right through five times in succession, and might have continued singing it all night if they had not been interrupted. 

So, this speech was the first thing that put the notion of revolution in the animals' minds. It incited the idea. Old Major dies three days after this. For the next three months, the animals discuss Old Major's ideas. Mostly it is the pigs who try to teach what Old Major had begun. Snowball and Napoleon discuss their different ideas about how to run the farm if a rebellion were to occur. After much speculation about a possible rebellion, an event occurs that actually inspires the rebellion. One night, Mr. Jones gets so drunk that he forgets to feed the animals. This incites the rebellion. Although it was not planned to begin this way, the animals break into the feed bins. Jones and his men retaliate but they are eventually driven off the farm. The rebellion has begun. 

There are other events and decisions which incite some change in the state of things. Perhaps most important is Napoleon's plot to oust Snowball from the farm. With Snowball gone, Napoleon becomes more and more powerful. He rules like a tyrant and the animals' lives are perhaps worse than they had been with Mr. Jones.