In "The Open Window," what causes Framton to leave the house?

Framton Nuttel is a stranger to the country and the Sappleton house. He has a letter of introduction from his sister so he can make acquaintances in the area. While waiting for Mrs. Sappleton, her niece Vera tells him a very creepy story about how her uncles were lost in a bog while hunting three years ago. She claims that her aunt leaves the French doors open just in case they ever come home. This...

Framton Nuttel is a stranger to the country and the Sappleton house. He has a letter of introduction from his sister so he can make acquaintances in the area. While waiting for Mrs. Sappleton, her niece Vera tells him a very creepy story about how her uncles were lost in a bog while hunting three years ago. She claims that her aunt leaves the French doors open just in case they ever come home. This sad tale is spun to make it seem as if the tragedy still haunts the house and Mrs. Sappleton's heart. Vera is a clever story-teller, though. She sets Framton up for the scare of his life by telling him about what the men were wearing when they left, as well as what Ronnie usually sings on his way back from hunting.

"Poor dear aunt, she has often told me how they went out, her husband with his white waterproof coat over his arm, and Ronnie, her youngest brother, singing, 'Bertie, why do you bound?' as he always did to tease her. . ."

These clues are exactly what sets Framton on the run from the house. When he sees the men coming and hears Ronnie actually singing the song, he takes flight. Vera set Framton up by providing him with specific details to what she witnesses every time the men go hunting; and when Framton hears the song, the text says, "Framton grabbed wildly at his stick and hat; the hall door, the gravel drive, and the front gate were dimly noted stages in his headlong retreat." Therefore, Framton leaves the Sappleton's house after being duped into believing a ghost story told by a young girl.