Answer:
Thurber conveyed humor in this story by making weird interpretations of the characters in the story. The next morning when Thurber met the American woman, he said, "The reason Duncan resembled Lady Macbeth's father as he slept is that it actually was her father!” “Good God!" breathed my companion softly. In this statement, Thurber attributed the death of the King to Lady Macbeth's father who appeared once in the story and this surprised the American woman.
Step-by-step explanation:
Thurber used humor in this story, a skill employed by writers to make the story fun and evoke laughter by giving unusual interpretation of events in the story. When the American woman was suspecting Macduff as the person who killed the King, Thurber came with an entirely different interpretation the next morning stating that it was Lady Macbeth's father who made just one appearance in the story that killed the King.
When the woman asked him who he suspected since he was going to buy Hamlet, he said "Everybody". These were funny and weird behaviors of Thurber.