After executing "traitors" with his private army of dogs, Napoleon begins to act as a dictator, appearing rarely and only with his dogs to protect him. In addition, he also has a black rooster that walks in front of them, crowing to announce his presence:
At the appointed time the animals would leave their work and march round the precincts of the farm in military formation... The dogs flanked the procession and at the head of all marched Napoleon's black cockerel.
(Orwell, Animal Farm, msxnet.org)
The black rooster marches ahead of all the other animals, and acts as the leader of a parade. The dogs surround Napoleon to protect him, and the rooster marches in front. This shows both Napoleon's mental movement into the role of dictator, as he is paranoid of attack and insistent on having public recognition, and his use of psychology to keep the other animals in line. They hear the crowing and know that Napoleon is coming, know that they must be good workers or they might be suspected of treason, and they remember the "knowledge" that has been drilled into them that Napoleon is a great leader who requires respect and deference.