In Chapter Seven of Animal Farm, the hens rebel against the pigs after Napoleon strikes a deal with Whymper who sell their eggs. As a result, the hens raise a "terrible outcry" and begin to lay high up on a rafter so that the eggs fall to the floor and smash.
For the hens, the selling of their eggs is tantamount to "murder" and this is why they choose to rebel. In addition, if we look back to Major's speech in Chapter One, being forced to lay eggs, which never had the chance to turn into chicks, is one of the reasons why the animals rebelled against Mr Jones and took the farm for themselves.
Similarly, in Chapter Five, the pigs protest Napoleon's decision to end the Sunday morning meetings. This is interpreted as a violation of their rights, hence their rebellion, which is quickly cut short by Napoleon's dogs.
The increasingly-dictatorial behaviour of Napoleon not only prompts the rebellion of these animals but also quells it. Protected by his dogs, Napoleon can crush the animals in a matter of seconds, as he does to the hens in Chapter Seven. After this, the animals have no choice but to obey his will.