Jeremy, a personal trainer at your local gym, you've never formally met but he always greets you by name, acting as if you two are old pals. His knowledge of your workout routine is oddly specific, and he refers to personal milestones in your life that you haven't shared with anyone. During a recent session, Jeremy's recollection of a particularly obscure event you attended struck a wrong note; he seemed to know details that were impossible for a stranger to know.