The sentence represents or demonstrates a foreshadowing (option B) in the story. Mr. White wished for 200 pounds, the monkey's paw moved (twisted) but the money didn't appear, then his son Herbert bets he'll never see it. Reading further, we learn that the paw's magic leads to tragic consequences for the people who asks for wishes to it. Herbert dies in a work-related accident and his company offers his family a compensation of 200 pounds, just the amount Mr. White wished for, and the same Herbert doubted he could see: his words were a hint the author gives us of what is to come in the story.
