2. The phrase "the cold wind in the stream is like a knife" describes the biting of the river and the cold of the autumn wind is like a knife. "Water" is biting cold, and "wind" blows on the face like a knife. The poet gave a detailed description of the ordinary scenery he saw in front of him, showing the feeling of biting cold outside the Great Wall, and also paving the way for the shocking bones and worn-out city walls below. Although "cold water" and "knife wind" are cold, they are not as miserable and desolate as before.