I DISMISSED THE THOUGHT IMMEDIATELY. NOT BECAUSE OF racial profiling. White women are as capable of craziness as anyone else. I dismissed the thought because of tactical implausibility. The timing was wrong. The New York subway would make a fine target for a suicide bombing. The 6 train would be as good as any other and better than most. It stops under Grand Central Terminal. Eight in the morning, six at night, a crowded car, forty seated, 148 standing, wait until the doors open on packed platforms, push the button. A hundred dead, a couple of hundred grievously injured, panic, infrastructure damage, possibly fire, a major transportation hub shut down for days or weeks and maybe never really trusted again. A significant score, for people whose heads work in ways we can’t quite understand.

But not at two o’clock in the morning.

Not in a car holding just six people. Not when Grand Central’s subway platforms would hold only drifting trash and empty cups and a couple of old homeless guys on benches.

The train stopped at Astor Place. The doors hissed open. No one got on. No one got off. The doors thumped shut again and the motors whined and the train moved on.

The bullet points stayed lit up.

The first was the obvious no-brainer: inappropriate clothing. By now explosive belts are as evolved as baseball gloves. Take a three-foot by two-foot sheet of heavy canvas, fold once longitudinally, and you have a continuous pocket a foot deep. Wrap the pocket around the bomber, and sew it together in back. Zippers or snaps can lead to second thoughts. Insert a stockade of dynamite sticks into the pocket all the way around, wire them up, pack nails or ball bearings into the voids, sew the top seam shut, add crude shoulder straps to take the weight. Altogether effective, but altogether bulky. The only practical concealment, an oversized garment like a padded winter parka. Never appropriate in the Middle East, and plausible in New York maybe three months in twelve.

But this was September, and it was as hot as summer, and ten degrees hotter underground. I was wearing a T-shirt. Passenger number four was wearing a North Face down jacket, black, puffy, shiny, a little too large and zipped to her chin.

If you see something, say something

I took a pass on the second of the eleven points. Not immediately applicable. The second point is: a robotic walk. Significant at a checkpoint or in a crowded marketplace or outside a church or a mosque, but not relevant with a seated suspect on public transportation. Bombers walk robotically not because they’re overcome with ecstasy at the thought of imminent martyrdom, but because they’re carrying forty extra pounds of unaccustomed weight, which is biting into their shoulders through crude suspender straps, and because they’re drugged. Martyrdom’s appeal goes only so far. Most bombers are browbeaten simpletons with a slug of raw opium paste held between gum and cheek. We know this because dynamite belts explode with a characteristic doughnut-shaped pressure wave that rolls up the torso in a fraction of a nanosecond and lifts the head clean off the shoulders. The human head isn’t bolted on.

It just rests there by gravity, somewhat tied down by skin and muscles and tendons and ligaments, but those insubstantial biological anchors don’t do much against the force of a violent chemical explosion. My Israeli mentor told me the easiest way to determine that an open-air attack was caused by a suicide bomber rather than by a car bomb or a package bomb is to search on an eighty- or ninety-foot radius and look for a severed human head, which is likely to be strangely intact and undamaged, even down to the opium plug in the cheek.

The train stopped at Union Square. No one got on. No one got off. Hot air billowed in from the platform and fought the interior air conditioning. Then the doors closed again and the train moved on.

Points three through six are variations on a subjective theme: irritability, sweating, tics, and nervous behaviour. Although in my opinion sweating is as likely to be caused by physical overheating as by nerves. The inappropriate clothing, and the dynamite. Dynamite is wood pulp soaked with nitroglycerine and moulded into baton-sized sticks. Wood pulp is a good thermal insulator. So sweating comes with the territory. But the irritability and the tics and the nervous behaviour are valuable indicators. These people are in the last weird moments of their lives, anxious, scared of pain, woozy with narcotics. They are irrational by definition. Believing or half believing or not really believing at all in paradise and rivers of milk and honey and lush pastures and virgins, driven by ideological pressures or by the expectations of their peers and their families, suddenly in too deep and unable to back out. Brave talk in clandestine meetings is one thing. Action is another. Hence suppressed panic, with all its visible signs.

Passenger number four was showing them all. She looked exactly like a woman heading for the end of her life, as surely and certainly as the train was heading for the end of the line.

Therefore point seven: breathing.

She was panting, low and controlled. In, out, in, out. Like a technique to conquer the pain of childbirth, or like the result of a ghastly shock, or like a last desperate barrier against screaming with dread and fear and terror.

In, out, in, out.

Point eight: suicide bombers about to go into action stare rigidly ahead. No one knows why, but video evidence and surviving eyewitnesses have been entirely consistent in their reports. Bombers stare straight ahead. Perhaps they have screwed their commitment up to the sticking point and fear intervention. Perhaps like dogs and children they feel that if they’re not seeing anyone, then no one is seeing them. Perhaps a last shred of conscience means they can’t look at the people they’re about to destroy. No one knows why, but they all do it.

Passenger number four was doing it. That was for sure. She was staring across at the blank window opposite so hard she was almost burning a hole in the glass.

Points one through eight, check. I shifted my weight forward in my seat.

Then I stopped. The idea was tactically absurd. The time was wrong.

Then I looked again. And moved again. Because points nine, ten, and eleven were all present and correct too, and they were the most important points of all.

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. Not practical for portable use. For portable use you need a battery, and for a linear yard of explosive you need some volts and amps. Tiny AA cells put out a weak volt and a half. Not enough, according to prevailing rules of thumb. A nine-volt battery is better, and for a decent kick you want one of the big square soup-can size cells sold for serious flashlights. Too big and too heavy for a pocket, hence the bag. The battery nestles in the bottom of the bag, wires come off it to the switch, then they head on out through an unobtrusive slit in the back of the bag, and then they loop up under the hem of the inappropriate garment.