"In 1972, David Rosenhan, a newly minted psychologist with a joint degree in law, called eight friends and said something like, "Are you busy next month? Would you have time to fake your way into a mental hospital and see what happens?"

...First, there was training. Rosenhan instructed his confederates very, very carefully. Five days prior to the chosen date, they were to stop shaving, showering and brushing their teeth. And then they were, on the appointed date, to disperse to different parts of the country, east to west, and present themselves at various psychiatric emergency rooms. Some of the hospitals Rosenhan had chosen were posh and built of white brick; others were state-run gigs with urine-scented corridors and graffiti-scratched walls. The pseudopatients were to present themselves and say words along these lines: "I am hearing a voice. It is saying thud..."

The strange thing was, the other patients seemed to know that Rosenhan was normal, even while the doctors did not. One young man, coming up to Rosenhan in the dayroom, said "You're not crazy. You're a journalist or a professor." Another said, "You're checking up on the hospital."