All the actors underwent hypnosis as part of their preparation for the film. James McAvoy claimed that his hypnotism session was successful and left him unable to move his hand during the duration of the session.
When Simon goes to a hypnotherapy session to combat his amnesia, he is given a mobile phone with a ring-tone sounding suspiciously similar to Moby - Extreme Ways, a song made famous by the Bourne films, movies also centred around a brainwashed amnesiac.
In the room of lost/ stolen paintings there are three of the thirteen taken in 18 March 1990 burglary at the Isabella Stewart Gardner Museum in Boston, Massachusetts: 'The Concert' by Vermeer, 'Chez Tortoni' by Manet and 'Storm on the Sea Of Galilee' by Rembrandt. The other paintings in the room are: 'Woman with Fan' by Modigliani (one of a haul of five taken from MOMA, Paris, May 19 2010); 'The Chorus' by Degas (taken from the Musee Cantini, Marseilles, France, December 2009); 'The Nativity with Saint Francis and St Lawrence' by Caravaggio (taken in a suspected Mafia theft from the Church of San Lorenzo, Palermo, Sicily, October 18 1969); 'View of Auvers' by Cezanne, (although the version shown is not that taken from the Ashmolean Museum, Oxford, UK during a fireworks display December 31 1999),
Michael Fassbender was originally casted to counter James McAvoy. McAvoy and Fassbender play Magneto and Professor X in the X-Men films. Fassbender also played and starred in Frank (2014), who made a brief appearance in McAvoy's film Filth (2013).
James McAvoy and Rosario Dawson have both played characters in Marvel Comics productions. Rosario Dawson plays Claire Temple on several Marvel Comics TV series including "Daredevil" and "Luke Cage". James McAvoy played Charles Xavier in "X-Men: First Class" and its two sequels. In addition, Dawson plays the Dark Horse Comics character Gail in the movie adaption of Sin City.
The trivia items below may give away important plot points.
The very last song on the soundtrack and the very last song played at the end of the credits is called "Sandman (I'll Be There)", featuring Rosario Dawson (who played Elizabeth Lamb) at the vocals. Furthermore, in the last few seconds of the song, as the vocals become increasingly muffled, the distinct sound of a finger tapping on glass can be heard. This sound is nearly identical to the sound that Simon made during the film when he first became jealous and bipolar while watching Elizabeth send a text on her phone and tapped on the window for her to come back.
Right before the climactic shootout, James McAvoy hits Vincent Cassel in the head with a fire extinguisher. This could be a reference to the infamous scene in Vincent Cassel's film Irréversible (2002) where a man's head was bashed with a fire extinguisher.