POINT NINE: MUMBLED PRAYERS. To DATE ALL KNOWN attacks have been inspired, or motivated, or validated, or invigilated by religion, almost exclusively the Islamic religion, and Islamic people are accustomed to praying in public. Surviving eyewitnesses report long formulaic incantations run through and repeated endlessly and more or less inaudibly, but with visibly moving lips. Passenger number four was really going at it. Her lips were moving below her fixed stare, in a long, panting, ritualistic recitation that seemed to repeat itself every twenty seconds or so. Maybe she was already introducing herself to whatever deity she expected to meet on the other side of the line. Maybe she was trying to convince herself that there really was a deity, and a line.

The train stopped at 23rd Street. The doors opened. No one got off. No one got on. I saw the red exit signs above the platform: 22nd and Park, northeast corner, or 23rd and Park, southeast corner. Unremarkable lengths of Manhattan sidewalk, but suddenly attractive.

I stayed in my seat. The doors closed. The train moved on.

Point ten: a large bag.

Dynamite is a stable explosive, as long as it’s fresh. It doesn’t go off by accident. It needs to be triggered by blasting caps. Blasting caps are wired with detonator cord to an electricity supply and a switch. The big plungers in old western movies were both things together. The first part of the handle’s travel spun up a dynamo, like a field telephone, and then a switch was tripped.