Trivia: Dustin Hoffman and Tom Cruise spent a lot of time with a man and his autistic brother, whom the man took care of much like the way Charlie has to take care of Raymond. A lot of the things Cruise and Hoffman did in the movie were things they witnessed the two brothers doing. One example of this was when Raymond and Charlie lean their heads against each other's at the end. Had Cruise and Hoffman not seen the brothers do that, it never would have been in the movie.
Trivia: The scene where Raymond freaks out over the fire alarm was added during filming. The director felt like too many good things were happening between Charlie and Raymond, and the audience might get confused and begin to believe Raymond is getting better, when there is no real way to get better from Autism.