ys (talking about the signalman), "There was something remarkable in his manner of doing so, though I could not have said for my life what." This brings in that sense of a mystery, because you don't know why he signal doesn't respond!
Also an interesting tension is made when it describes how the narrator goes down the steep slope to where the signalman is. "The cutting was extremely deep, and unusually precipitous. It was made of a clammy stone that became oozier and wetter as I went down." This gives you that unwelcoming, cold, damp feel to the place.
The characters themselves were very mysterious. Even at the beginning when it seems the signalman is looking at the tunnel for something that isn't there, and also how it never mentions once in the book why the signal man was actually there in the first place, and weather by unnatural causes he was somehow driven there, also you don't get any details about him or his live in the story. You can almost imagine him as just an illusion. The signalman in the story is perceiv
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