The thirteenth story

I know that feeling at the back of the neck is somewhat common, but this is the first time I have experienced it. Like many loners, my senses are accustomed to the presence of others; I am used to being the secret observer in the room more than being observed. And now someone is watching me, not only that, but they have been watching me for some time. How long has this undeniable feeling been tickling me? I contemplated the last few minutes trying to trace my bodily memory with the events of the book. Was I being watched since the nun started talking to the young man? Since I was guided inside the house? Or before that? I tried to remember without moving a single muscle; I was focused on the page as if nothing had happened.