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.