What is the theme or author's point for writing "The Open Window"?

In the short story, "The Open Window," by Saki, the author
writes to entertain. That is the point of the author's story. He uses Vera, a
mischievous niece, to tell a tall tale, that frightens Framton Nuttel. Overall, the
story is entertaining from the beginning of Vera's tall tale until the end of the tall
tale. Not only is Mr. Nuttel afraid when the three men begin walking toward the open
window, but the reader is just as uneasy.

The short story
offers not only entertainment, but it offers insight into the heart of mankind. The
theme is deception. Without the niece's deception, there would be no
story:

Were
it not for deception, this story could not happen. The action and irony of the story
revolve around the apparent deception that Mrs. Sappleton's niece practices. It remains
to be seen, however, whether this deception is a harmless prank or the result of a
sinister disposition. If the niece's deception is cruel, then the reader must question
the motives behind the deception practiced by all tellers of stories, including Saki
himself.

Also, the theme of
appearance versus reality is evident in this story. Can it be for real that these men
are walking toward the open window after four years of being missing. What is real and
what is not real:

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When Mr. Nuttel (and the reader) are presented
with a contrary reality at the end of the story, the result is a tension between
appearance and reality that needs to be resolved: Which is real? Can they both be
real?

Finally, there is a
theme of sanity versus sanity. There is a fine line line between the two. Is Mr. Nuttel
losing his mind right along with Mrs. Sappleton? Apparently, he can see what she can see
and should not be seeing:

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Nuttel's susceptibility to deceit is no
different from that of the reader of the story. Yet Mr. Nuttel is insane, and the
reader, presumably, is not. In order to maintain this distinction, Saki forces his
reader to consider the nature of insanity and its
causes.

The above themes
entertain the reader and keep the reader in suspense until the end of the Vera's tall
tale.