Parry is natural language program that simulates the thinking of a paranoid individual. This thinking entails the consistent misinterpretation of others motives – others must be up to no good, they must have concealed motives that are dangerous, and their inquiries into certain areas must be deflected - which Parry achieves via a complex system of assumptions, attributions, and "emotional responses" triggered by shifting weights assigned to verbal inputs.
Parry was the first to pass the Turing Test - it was in the early seventies, when human interrogators, interacting with the program via remote keyboard, were unable with more than random accuracy to distinguish Parry from an actual paranoid individual.