In "The Open Window," why does Vera enjoy tricking people?

Vera is an example of how a skillful fiction writer will create a character to fit the needs of his plot. Such examples are to be found throughout the world's literature. Characters are not real people but illusions. The three characters in "The Open Window" were all created to fit the parts they needed to play. Framton Nuttel is a neurotic man who is only visiting the Sappletons because he has come to this part of the country for a "nerve cure." He doesn't know a thing about the Sappleton family or about the region. Mrs. Sappleton is an empty-headed woman who has no internal or external resources. She is as confined as a caged bird or a house cat. She is devoted to the three men in her life and has learned to talk their language, which is all about tramping around in the mud and killing birds. Saki needed a character who would tell the neurotic visitor a wild ghost story and set him up to be terrified when the three hunters appeared. The author invented a girl who was just young enough to be mischievous and just old enough to be believable. She is the best character in the story--but she is just a character and not a real, live human being. We can only speculate about her reasons for being slightly sadistic.

Vera is a girl. She can't go hunting and is confined to the house just like her aunt, and she may see her future in her aunt. She will get married and have to play hostess to unattractive men like Framton Nuttel and idiotic women like her aunt. If she marries a wealthy man she will have servants to do all the work, and she will have little to do except to read books and listen to male talk. Vera must feel resentful. She is introduced as a stand-in hostess while her aunt makes a few last-minute touches to her hair and dress. No doubt Mrs. Sappleton has sent Vera on ahead in order to give the girl some practice for the role of hostess she is destined to assume in the not-too-distant future. Vera knows this and resents it. She doesn't want to be another Mrs. Sappleton. Who would? Since Vera has virtually nothing to do but read, she has augmented her own vivid imagination with ideas she has picked up from her books. She suffocates in an environment she would like to escape from, so she might like escapist literature.

So Vera is resentful, bored, imaginative, and addicted to escapist reading as well as escapist fantasies. She resents being kept a prisoner in this country manor where everybody predictably does and says the same things day after day until they are driving her insane. She takes out her resentment and frustration on poor Framton Nuttel because he doesn't know anything about anybody in the region. She may not have intended to send him flying out into the night. If he had stayed, he would have met the three men and quickly realized the girl was only playing a practical joke. He could not have caused her trouble by repeating her ghost story. He might have given her a dirty look, and she might have returned it with a winsome conspiratorial grin. But because the author had created a "patsy" who was already a nervous wreck, Framton reacts more vigorously than the girl probably expected, and she has to invent another story as a cover-up.

"I expect it was the spaniel," said the niece calmly; "he told me he had a horror of dogs. He was once hunted into a cemetery somewhere on the banks of the Ganges by a pack of pariah dogs, and had to spend the night in a newly dug grave with the creatures snarling and grinning and foaming just above him. Enough to make anyone lose their nerve."