Continuity mistake: In the scene where Debra tells Ray her parents have separated and he laughs, later on in this scene he tells Debra that he got free candy from the broken vending machine at work. When Debra leaves the room, Ray starts taking more candies out his pockets and throwing them on the bed. Take notice of the position of the sweets on the bed. Now just after the close up scene of Ray scratching his head, look at the position of the sweets. Totally different. One or two are actually closer to the end of the bed, whereas in the scene before, they were more further on. (00:52:50 - 00:53:55)
Revealing mistake: Marie acts like she is reading from Raymond's diary, however from the angle that she's holding it, it's obvious that there's no writing on the page except for a standard header on every page. Raymond also doesn't write anything when she asks him to amend the entry.
Factual error: Ray, Gianni, Robert and Frank are watching a football game when Ray gets the call from Newsday to cover the Friday press conference for the Super Bowl that weekend. There is a 2 week break between the AFC/NFC championship games and the Super Bowl, so there would be no NFL game on TV at the time. There would also be no NFL game on during the afternoon on a weekday.