Bruce can tell what's coming as soon as Tony licks his lips, and he wars with himself briefly. Does he trust Tony? Of course he does. Does he trust Tony's impulse control, especially when he's a new vampire who's never fed? Not so much. It'd be easier if his blood wasn't so potentially dangerous -- not that he's ever tested it on a vampire; maybe it wouldn't hurt anything -- but that's what makes this extra frightening.

Still, he doesn't move. He closes his eyes and stays tuned into everything Tony does, but he stays perfectly still.