The thirteenth story

I know that the feeling in the back of the neck is somewhat common; but this is the first time I experience it. Like many loners, my senses are used to the presence of others, so I am accustomed to being the hidden spy in the room more than being spied on. And now someone is watching me, and not only that, but has been watching me for some time. How long has this unmistakable feeling been teasing me? I contemplated the last minutes trying to trace my body's 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 engrossed in the page as if nothing had happened.