Mark watches, keeping to himself, and eyeing the bugs. A few of them, he can't exactly tell the difference between, but he doesn't question. He's seen tiny differences in films that no one else has been able to see. It's all in what you're trained, or what you've trained yourself to see. He actually is a bit more interested in Grissom himself, the way he goes about pinning the bugs, and how he deliniates the different types.