Deliberate mistake: During the interrogation scene, a patient asks for a glass of water. When she receives a the glass of water, she lifts her right hand to her mouth and makes a drinking motion, but is not holding a glass. A moment later she sets down an empty glass with her left hand. When the camera angle changes, the glass has become half full. This implies the patient's mental instability and adds to the surreal feel of the film.
Deliberate mistake: The two princesses do not age, despite the film's story occurring over several years.
Deliberate mistake: Elise goes to the "Gare de Lyon" and takes a train that goes to Venice (an italian ATR - AV, a high speed train). The only direct train to Venice is a sleeper train, in addition the travel time (over 8 hours) required would make the use of a high speed implausible. Furthermore these trains are not running in France, "the connecting" railroad is still under costruction.
Deliberate mistake: During some shots seen from the camera when Aron is filming his diary the camera performs some subtle movements to keep him in frame. These movements are from a tripod as they're too subtle and controlled to be from someone operating the camera with one arm and moving around as much as James Franco was.
Deliberate mistake: The (fake) confession letter was postmarked from Ohio and sent to Allison Connor, 331 Henry Lane in Hilliard, MB 21243. No U.S. state has a postal abbreviation of "MB." The way the "B" was written in thick bold letters made it resemble a "D" - "MD" represents Maryland (where the film apparently takes place). Also, there is no current 21243 zip code in the U.S. There is a 21241 for Baltimore City and the next consecutive zip code is 21244 in Baltimore County. The created address LOOKS real. (00:50:44)