His attention stays on her. These slides aren't new to him, at this point - he's been squinting at them for the last day. What is new is seeing Agent Scully react to them; this is a test of sorts, of her commitment to her new work.

And so far, he has to admit she seems engaged. "The county coroner couldn't tell us. All we have to go on is the substance found in the surrounding tissue."

Click.

"Recognize that molecule?"