A train car moving at high speed with the doors and windows closed is a violent psychopath’s dream—a veritable barrel full of unarmed, unsuspecting fish. Most of us have our heads buried in our phones, our ears distracted by music or podcasts. Some of us are poring over newspapers or dreamily watching the countryside fly by. Rarely do any of us do a threat assessment of those nearby. We are in our own little in-between place—not home, not at work. En route. Vulnerable.