I think that zarrof thinks that because rainsford chooses his prey and cares about what animal he kills. its something like that.
hope it helps!
The passage used a combination of comparison and contrast and: <span> C. cause and effect.
</span>The passage give us a well descriptive explanation on how the microorganisms (the cause) developed in such a way to the point where their fossils ended up as a petroleum/coal (effect)