Pigs have a reputation in our society for being dirty. The word pig is also used to describe anyone who is greedy.
In our society, the word pig is used derogatorily to refer to anyone greedy and selfish. We use the term pig to refer to a person who eats too much, or is otherwise brutish and low-mannered.
However, pigs are also a greatly misunderstood animal. While many people think they are dirty and disgusting, evidence shows that they are actually very intelligent. All of these things make them the perfect animal to represent the manipulative communist leaders in Animal Farm.
They are dirty and greedy... that's what lots of people think of them.