1/2
[See, normally Sebastian would know well in advance if someone was approaching. Not the who, necessarily, but at least that it's a person.
Right now he's occupied with trying to will the room not to spin, and thus only realises he has company when Chloe speaks up. He doesn't startle, exactly, because Sebastian doesn't do big gestures like that, but he's still noticably surprised by the voice. Ah...]