When the General tells Rainsford that it is man he hunts, Rainsford reacts with?

From the text:

"But no animal can reason," objected Rainsford.
"My dear fellow," said the general, "there is one that can."
"But you can't mean--" gasped Rainsford.
"And why not?"
"I can't believe you are serious, General Zaroff. This is a grisly joke."
"Why should I not be serious? I am speaking of hunting."
"Hunting? Great Guns, General Zaroff, what you speak of is murder."