What are examples of foreshadowing in "The Open Window" by Saki?

In Saki's "The Open Window," there is foreshadowing—defined as clues that suggest events that have yet to occur—soon after Vera enters the room where Framton Nuttel awaits her aunt. Nuttel is unsure if such a visit with a stranger will do much for a nerve cure for him. When she asks Framton Nuttel if he knows the people from the area and if he knows much about her aunt, Nuttel answers "Hardly a soul."

At the time that Vera, "the very self-possessed young lady of fifteen," asks Nuttel if he knows anyone from the area and if he is acquainted with her aunt, Mrs. Stappleton, she wants to determine to what lengths her "[R]omance at short notice" can go. Therefore, after Nuttel replies that he knows almost no one in the area, Vera realizes that she can give full rein to her imagination and take advantage of the nervous little man across from her. Cleverly, she proceeds to weave a tale that has some veracity mixed in with fictitious tragic events.

Knowing that Mr. Stappleton and his wife's brothers will soon return from their outing, Vera tells Nuttel that he has arrived, coincidentally, on the "tragic anniversary" of the disappearance of Mr. Stappleton and Mrs. Stappleton's two young brothers, who went hunting but never returned. She weaves a horrific tale of their apparent deaths that Mrs. Stappleton is unable to accept. Instead, Vera claims Mrs. Stappleton continues to hope they will return. Using this backstory, Vera devises an explanation for why the window is open: "each evening the window is kept open until dusk" in the hope that the men will return through it.

As she expresses her pity for her "poor, dear aunt," Vera tells Nuttel that her aunt often relates how Ronnie, her youngest brother would sing, "Bertie, why do you bound?" She adds,

I almost get a creepy feeling that they will walk in through that window—

and then stops abruptly as Mrs. Stappleton finally enters the room. As Nuttel explains why he has come, Vera's aunt stifles a yawn. Then, she abruptly interrupts, "Here, they are at last!" adding that "they" are just in time for tea. When a voice chants, "I said Bertie, why do bound?" Vera feigns a "dazed horror" and a terrified Framton Nuttel rushes out of the house.