You’ve seen it yourself, sometimes in public, perhaps on a subway car. Somebody starts to act strange. He talks to himself, wanders the aisles and mutters.

Bystanders freeze. Their muscles tense, and their eyes become nervous. If they stare at him, will it somehow provoke him? Has he a knife or a gun on his person? Could a gesture or word set him off? If they pretend that he’s normal, might he not just go away?