There is an important difference between animals and human beings. All human beings do not behave alike. Each one has a different conduct and behaviour. Different human beings respond differently under the same circumstances. However, most animals confirm to similar behaviour under the same circumstances. The reason is that animals follow their natural instinct and a simple sense. However, human beings are complicated and think a lot and create a lot of knowledge in their mind, which makes a person behave in a different way than others.
Animals do not get angry or aggressive just like that. The are usually peace loving. When they sense danger then they turn aggressive. People can turn aggressive, all by themselves, without being provoked too.
Some animals fight directly using their force and pace, when they are aggressive against another. They may not attack from behind or think of cheating ways. Human beings may cheat, or collect support of other people or animals. Animals fight with aggression all by themselves.
Animals cannot think at all, when they are aggressive. Human beings can control themselves and can make many decisions. Human beings can also change their decisions quickly. Animals cannot do that. Some times animals cannot evaluate whether they have an upper hand or not.
That is why, some times people say that, a person becomes an animal when he/she is angry or aggressive. Human beings can learn to control themselves and become better persons.