Walter is examining the still-smoking body of one of the victims and happily nattering away about how he once had a watch similar to the one the corpse, which was given to him by his Uncle Henrich, who loved rhubarb and he's interrupted by a woman standing nearby, asking, "Am I gonna die?" She gives it enough attitude to convey that she'd LOVE to hear more about Uncle Heinrich and his legendary love of rhubarb, but she'd rather not be reduced to ashes herself so maybe he can focus on the task at hand. Walter's startled. I think he'd managed to block out the silent living statues. But he does say he can't answer her yet. "What are you?" asks the red-haired woman, who you might remember as Charlotte Lewis from Lost, as the J.J. Abrams pipeline continues.
Confused, Walter explains that he's human and then asks what she is: "Is this some sort of alien invasion?" She clarifies that she just meant what is he doing here -- is he a doctor, etc. He says he's a scientist and then walks over to her to ask if he can take a blood sample. "The discomfort will only be temporary," he assures her. "That's what all you men say," she says and Walter lets himself smile. I think I may have just fallen in love a little with the knockout with the English accent and the beautiful red curls and enough bravery to, even as she's in danger of dying, mock every man she's ever slept with.
Walter starts getting her arm ready and then notices some black smudging on her fingers. He asks where she got it, and she doesn't know -- possibly the escalator.
Next thing we know, FBI agents are coming the escalator for clues while Astrid checks out the woman's blood sample; she says it shows signs of a foreign incursion at the cellular level, but to determine if it's viral, they'd have to get it back to the lab to be sure.
Until then, it probably does no harm to talk to the blood sample as Walter starts to do, asking what sort of virus it is: "If you were aerosolized, you would have infected everyone, not just those on the escalator. If you were harbored on a water tap or a doorknob, the first few contacts would have wiped you clean. What would have kept you fresh and so infectious, my lethal friend?"
Then an FBI technician working under the floor panel that services the escalators says that he's found something and Astrid and Walter come over and find some sort of machine clipped to the mechanism underneath. "Oh dear. This is not a virus at all," says Walter.