The paper pinned over the door is a barrier, like the ones Anderson throws around. It gives this room the protection that a home would have: a vampire can’t enter without the owner’s express invitation.
Jon still has a faint scar on his arm from that nine-year-old ghoul bite.
Seras: Please, try not to strain yourself. What’s the last thing you remember?
Jon (thinking): Cute nurse…No! Cute is bad. Cute will distract you into saying something stupid.
Jon: Listen, it’s all pretty blurry, okay? I was with my friend, and I had skipped one of my pills. That’s probably why I fainted. Please, can you just tell me if he’s here?
Seras: Persistent, aren’t you? All right, come in!