This hallucination of Ed Harris is the key factor in Nash's delusional thinking. He has delusions of being a secret government aide that is helping the U.S. find bombs throughout the country that were placed here by the Russians. Nash hallucinates that Ed Harris places a device inside his arm that allows him to see a code under an ultra-violet light. This device allows Nash to gain entrance to a secret location where he is to leave the cracked codes. In reality this secret location is an abandoned, dilapidated mansion, and the key- pad that Nash types his code into no longer functions. Nash's code breaking abilities are partly made possible by his hallucinations. The codes pop out of the paper to him and everything makes sense. Even though the codes are imaginary since there was no secret- code- breaking- project underway, Nash figures out mathematical formulas and actually modifies a theory that had been accepted in its field. He says that he can't do his work without the hallucinations.
One scene that will remain in my mind forever and the best example of the negative symptoms of Schizophrenia is a scene where John Nash is shown holding his infant son while the baby is crying and Nash shows absolutely no sign of emotion at all. This is just one example, although a loss of feeling is one of the most predominate negative symptoms. Nash's flat affect is seen through out the film in many instances but that scene that shows him holding the baby shows