In "The Open Window," why did Framton Nuttel dash off without a word when he saw Mr. Sappleton and Mrs. Sappleton's brothers approaching?

Framton Nuttel is completely taken in by Vera's story. The same applies to the reader, who believes that the three men approaching the open window must be the ghosts of the three male relatives who died three years ago after being sucked into a bog. Vera knows that her giddy aunt will be sitting there waiting for her men to return for tea and will be talking about nothing but shooting birds. Vera convinces Nuttel that her aunt lost her mind three years ago when the three hunters were killed along with their spaniel. The aunt is expecting the return of hunters who have been dead for three years. Vera is prepared to put on an expression of horror when her aunt finally sees the men she is expecting. Framton is seated in such a way that he looks at the aunt first, then at Vera with sympathy to show he understands the poor woman's mental condition, then quickly at the open window when he sees the "dazed horror" in Vera's eyes. Vera has given him a number of bits of description by which he will immediately recognize the three men as the ones who are supposedly dead.

In the deepening twilight three figures were walking across the lawn towards the window, they all carried guns under their arms, and one of them was additionally burdened with a white coat hung over his shoulders. A tired brown spaniel kept close at their heels. Noiselessly they neared the house, and then a hoarse young voice chanted out of the dusk: "I said, Bertie, why do you bound?"

Vera is bored to tears by the sameness of life in this English country manor. She is vindictive because she feels like a prisoner. She has heard Ronnie singing, "Bertie, why do you bound?" so many times that she can be sure he will sing it again this evening as he nears the big house. The white coat and the brown spaniel are also unmistakable identifying cues. At this point the reader understands the terror that makes Nuttel jump up and flee for his life. They are not only ghosts but ghosts armed with guns! It is not until Nuttel has fled the scene that the reader learns that the whole incident was a practical joke.

"Here we are, my dear," said the bearer of the white mackintosh, coming in through the window, "fairly muddy, but most of it's dry. Who was that who bolted out as we came up?"

"A most extraordinary man, a Mr. Nuttel," said Mrs. Sappleton; "could only talk about his illnesses, and dashed off without a word of goodby or apology when you arrived. One would think he had seen a ghost."