Because Hamlet has apparently gone mad, it is not strange for the other characters to find his statements confusing or nonsensical. Hamlet (and Shakespeare) takes advantage of this by answering in humorous ways when facing these characters directly. While his statements are often incomprehensible to the other characters, both the audience and Hamlet find them funny. Moreover, they are used as a mechanism by which Hamlet is able to deflect questions and avoid facing the consequences of his actions.
