What is General Zaroff's main reason for preferring to hunt human beings rather than animals?

General Zaroff was bored with hunting animals because they couldn't reason. He wanted the hunt to be more difficult...... more of a challenge.

I wanted the ideal animal to hunt," explained the general. "So I said, `What are the attributes of an ideal quarry?' And the answer was, of course, `It must have courage, cunning, and, above all, it must be able to reason."'