Final answer:
In 'The Adventure of the Speckled Band,' Helen Stoner hears a low whistling sound at night when she begins sleeping in her sister's former bedroom. This sound is an important clue in the unfolding mystery of the plot.
Step-by-step explanation:
In "The Adventure of the Speckled Band," when Helen Stoner begins sleeping in her sister's former bedroom, she hears a low whistling sound in the dead of the night. This sound becomes a pivotal clue in this Sherlock Holmes mystery. Helen's experience in the room is shrouded with tension and fear, akin to the feelings evoked by various eerie noises described in other literary excerpts. The noises range from the clicking of an opening door, the haunting calls of wildlife, the creaking and the crackling reminiscent of tension-filled scenes, to shadowy perceptions under the influence of a storm, and the deep sense of dread that certain ominous sounds can provoke in the stillness of the night.
The sounds heard by Helen Stoner are not explicitly described as either a whistle or a low whistling sound, but it is strongly implied due to the repeated description of a whistle throughout the story. The nocturnal ambiance characterized by such sounds is significant in literature as it often heralds key plot developments or reflects the inner turmoil of the characters, as is the case in The Adventure of the Speckled Band.