Ruby watched the vampire consider what to do. Torn between taking the chance, torn between attacking Sam, or her, But Tanya was spooked still by his calmness, she suspected there was more to it. Suspect there was some other plan and maybe following what the guy wanted. Maybe it would lead to a way out of this. Or maybe she'd die quicker.
Ruby saw the moment the decision was made and Tanya hit him. With all her vampiric strength, Ruby's eyes narrowed in spite of herself and she looked away just for a moment, just to a window leading into the bar bathroom, a flash of brunette hair enough to let her know the slayer had seen it. Ruby met her gaze just for a second in a moment of understanding that Sam needed this before the girl vanished leaving them to it.