"The Open Window" by Saki is one of my favorite short stories. I absolutely love a story that makes me say "Wow!" at the end: the surprise is everything.
In this short story, there are probably several things that are going on. Mr. Framton Nuttel has come to the country to rest: hopefully a cure for the nervous condition from which he suffers. It is ironic that a man comes to the country for his nerves and ends up worse off than when he arrived. It is also ironic, I find, that someone from the city who is dealing with much more sophisticated, high-paced life-style can be so taken in—but perhaps Mr. Nuttel's nervous condition might excuse his lack of insight. So we have this nervous city man visiting, and he is left alone in the company of the clever, but seemingly sweet, fifteen-year-old Vera.
This is the second major "piece" to this storyl. Perhaps with only the company of her mother and several older men of the family (uncles and cousins), Vera has found a need for a personal outlet: something that will entertain her as she cannot fit into the man's world surrounding her, and an opportunity to hone her story-telling skills. Her tale is very convincing, while her trick rather unkind. When the story is over, we may be slightly amused by the practical joke Vera has played, but I would expect that Saki is entertained by the precocious nature of Vera—and not just the gullibility of Mr. Nuttel, but perhaps that of the reader, too, who may well never have suspected a thing when first hearing Vera's "horrifying" tale.