In "The Open Window," why is it significant that Framton Nuttel is described as undergoing a "nerve cure"?

In the story, Framton Nuttel is described as undergoing a "nerve cure." This is significant because it highlights Framton's hypochondriac tendencies and foreshadows his later, agitated response to Vera's elaborate story. In other words, this mention of Framton's "nerve cure" sets the stage for how Vera's story will affect Framton. Thus, our enjoyment of Saki's story will definitely be heightened when we read of his paranoid actions later in the story.

Accordingly, Vera concocts a gothic story about Mrs. Sappleton's husband and two brothers, all supposedly lost three years ago when they became "engulfed in a treacherous piece of bog" while snipe-hunting. Vera ends the story on an ominous note, musing that, on quiet evenings, she sometimes imagines that the three men will walk in through the tall French window that overlooks the lawn.

Meanwhile, Framton later bores Mrs. Sappleton with anecdotes about his numerous "ailments and infirmities." He attests that the doctors have ordered "an absence of mental excitement, and avoidance of anything in the nature of violent physical exercise" for him. Subsequently, the irony is apparent when Mrs. Sappleton's husband and two brothers do eventually walk in through the French window. Framton's nerves are then so violently excited that he cannot make his getaway fast enough.

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. A cyclist coming along the road had to run into the hedge to avoid imminent collision.