According to Freud’s humor theory， the cause of the humor lies in the supposition that the expectations the readers have towards the characters or the events in a novel have not been realized so that the disagreements between the readers’ expectations and the unexpected development of the story brings about humor. In the following the two disagreements represented in the tradition of con men will be analyzed.
　　1. The disagreement between the con men’s words and deeds
　　In Chapter Twenty， the young con man called himself “the rightful Duke of Bridgewater”， which actually was totally a lie. But the old con man knew that “Duke” was lying and decided to call himself “the King”. Besides， he mistakenly called the young man “the Duke of Bilgewater” which means the dirty water. The “Duke” and “King” have not realized that this is a satire but the readers understand the meaning with a laugh. In here， Twain successfully uses pun for the purpose of satirizing con men and producing the effect of humor. Through his skillful use of humor， Mark Twain also pokes satire at a number of human flaws， such as gullibility and idiocy. In Chapter Twenty， in a camp sermon meeting， “the King”， in the guise of a pirate for thirty years in Indian Ocean， lies that he is robbed but ready to turn the Indian pirates into right path for the reason that he is moved by the preacher’s sermon. His speech is really inciting and fraudulent： “Don’t you thank me， don’t you give me no credit；it all belongs to them dear people in Pokeville camp-meeting， natural brothers and benefactors of the race， and that dear preacher there， the truest friend a pirate ever had （172）！” The king’s tearful speech and the following donation from his audience can be seen as a terrific caricature.
　　2. The disagreement between the situation of the con men’s frauds and the set-up of the actual circumstances
　　Twain portrays the victims of the con men’s schemes as unflatteringly as the con men themselves. The duke and the king’s production of the “great” Shakespearian plays， for example， is a complete farce， a brief and ridiculous show for which the audience is grossly overcharged. However， what makes the con men’s show a real success， however， is not any ingenuity on their part， but rather the audience’s own selfishness and vindictiveness. Rather than warn the other townspeople that the show was terrible， the first night’s audience would rather see everyone else get deceived in the same way they did. Thus， the con men’s scheme becomes even more successful， which actually shocks the readers as a result of the unexpected consequence of the con men’s frauds， at the same time producing the profound humorous and satirical effect. Therefore， the readers can see that although the con men’s audacity and maliciousness are sometimes shocking， Twain’s portrayal of the victims is often equally unsympathetic.
　　To sum up， the novel is full of malicious lies and scams， many of them coming from the duke and the king. It is worth mentioning that the innocent Huck himself tells a number of lies and even cons a few people but he does it for the good purpose of protecting Jim. Through these kinds of disagreements， Twain successfully employ the humor this kind of writing technique to describe the characters vividly and impressively， to deeply disclose the ugly social realities and the vicious racial discriminations of the then American society， and to express his deep concern about his people and the problems of his country to be solved.