Johnny Depp's line, "This is not my beautiful house. This is not my beautiful wife. Anymore.", is taken from the Talking Heads' song "Once in a Lifetime".
When Johnny Depp's character drops the hat on his desk, a copy of Hunter S. Thompson's "The Rum Diary" is visible on the table. Depp is slated to play in the motion picture version of the book, The Rum Diary.
Johnny Depp's character's name is Morton Rainey. Toward the end of the movie, this character puchases three items at the grocer's. One of the items is a box of MORTON's salt whose moto is: "When it rains it pours." Thus Morton Rainey.
In the scene where Johnny Depp bursts in on Maria Bello and Timothy Hutton in the Motel; David Koepp wanted Bello and Hutton to look shocked and scared - he made them both lie in the bed for 15 minutes before Depp rushed in. The production crew set up large speakers that blared static noise when the script called for them to be scared. The lights in the room were also rigged to go on when Johnny Depp opened the door, startling the actors further. No one knew exactly how to act.
Mort explains to John Shooter, in his defense, that his story is the original and was published originally in the June 1995 issue of Ellery Queen's Mystery Magazine. Ted Milner (Timothy Hutton) tells Mort that he's from a town called Shooters Bay, TN, adding doubt in Mort's mind about Ted's real intentions. Timothy Hutton's father, Jim Hutton, portrayed Ellery Queen in the 1975 TV series. Ellery Queen himself was the son of a police detective and the writer of mystery novels as well as an amateur detective.
The trivia items below may give away important plot points.
When Mort's conscience is revealing the real situation to him at the end of the movie, Mort begins to yell, "Rah! Rah! Rah!" Johnny Depp took this from his son, who was pre-verbal and expressed his confusion by saying "Rah!" Depp felt that Mort would be so confused at that point that he would not know what to say to convey what was happening that he would become pre-verbal again.