When I was a 14-year-old in a suburb of Dublin, we were at the height of “the Troubles.” During this period of civil unrest, our school regularly took in girls from Northern Ireland to get them away from the bomb blasts and shootings in Belfast, some two hours' drive across the border. One of these girls was named Sandra, and she had been at our school for a couple of weeks when one day the two of us decided to walk home for lunch. As I was walking and chatting, I suddenly became aware that Sandra was no longer beside me.
Looking around, I saw her about 10 meters back, lying flat on the pavement. A car had backfired, and she had instantly thrown herself on the ground. Deep in her brain, an alarm signal had gone off. That same signal had slipped past me unnoticed.