He relaxes somewhat when she pulls away. There's no trace of revulsion in the way he reacts to her, just confusion. Severus understands that she's not trying to get closer to him to stick a knife in, but he doesn't have anything else to supplement that with. (He also isn't having any kind of hyped up adrenaline reaction because he isn't afraid.)

"You should go to the communications center and see if anything else comes up," he tells her, evenly. "I can walk you down there if you like."

Severus sounds perfectly fine about doing that. Maybe Darcy will piece together that he doesn't like being touched without warning one of these days.