On an April morning in 2001 Christopher Bono, a clean-cut, well-mannered 16-year-old, approached Jackie Larsen in Grand Marais, Minn. His car had broken down, and he needed a ride to meet friends in Thunder Bay. As Larsen talked with him, she came to feel that something was very wrong. “I am a mother, and I have to talk to you like a mother,” she said. “I can tell by your manners that you have a nice mother.” Bono replied: “I don’t know where my mother is.” After Bono left, she called the police and suggested they trace his license plates.

On July 1, 2002, a Russian Bashkirian Airlines jet’s collision-avoidance system instructed its pilot to ascend when a DHL cargo jet approached in the Swiss-controlled airspace over southern Germany. Nearly simultaneously, a Swiss air traffic controller—whose computerized air traffic system was down—offered an instant human judgment: descend. The Russian pilot overrode the software, and the plane began to angle downward.

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