He was not surprised because he was already going insane. Since he was hallucinating that the raven was spouting words at him. He was already ill to begin with so it was not a surprise he thought the raven spoke.
There are different evaluative questions that we can ask to that excerpt. But, one crucial point must bind these questions. The questions have to be personal. One example could be:
According to the excerpt, do you think Mr. Yallow has to be held responsible for the actions of Graciella?
Answer: how is this a question i dont understand.
Explanation: