When Philippe bites the jawbreaker and breaks teeth, the jawbreaker is on the right side of his mouth. In the next scene, he goes into the dentist's office holding the left side of his face.
Philippes right shoe sole is considerably bloodied when he kneels down on the wire. However, during several shots afterwards and before, it is never seen bloodied.
The injured foot of Philippe should have left more blood on the wire than actually appeared in the movie, where blood is seen on the wire in only one of two shots.
On August 8th, the sunrise in New York City was at 5:59 a.m., which means twilight was at 5:30 a.m., less than half an hour later, as shown in the movie.
Atop a tall building like that, there is always a lot of wind. However, we can't see any hair blowing or things disturbed by wind when they are on the top.
On August 8th, sunrise in New York City was at 5:59 a.m., which means twilight was at 5:30 a.m., not more than an hour later, as shown in the movie.
American calendars begin on a Sunday; so American viewers might get the impression that the August 6, 1974 shown on the calendar was a Monday. However, the calendar shown is French, which correctly indicates that August 6, 1974 was a Tuesday ("Mardi").
(At 54 minutes) During Philippe and Annie's argument, Charlotte Le Bon silently mouths Joseph Gordon-Levitt's lines while he is shouting at her.
In the bird's-eye view of the Twin Towers on the poster and the DVD cover, each of the towers has its own vanishing point, a geometric impossibility. All vertical lines should meet in only one imaginary point directly under the viewpoint. This may have been done deliberately by the art department in order to make the wire stick out which would otherwise be camouflaged by the buildings' lines.
In the Italian translation, when Philippe asks "what gives 81 divided by 3?", the other guy replies 37 (!)
The broadcast antenna on the World Trade Center's north tower wasn't added until 1978, four years after the events of the movie took place.
The characters are seen exiting a subway station of the J M Z line. The Z line didn't exist until 1988.
On the last shot of Lower Manhattan, at the end of the movie, you can still clearly see it is supposed to be 1974. Battery Park City hasn't been built. However, on the right you can clearly see the round glass building of 17 State Street, which was built between 1983 and 1987.
The Subway entrance near the WTC sports a livery that did not appear until the 1980s.
The J and M Lines' route emblems were not colored brown until 1979. In 1974, the J's emblem would be dark grey, while the M's would be light blue.
St. Paul's Chapel is incorrectly oriented, as it is shown to face west, toward the Twin Towers. St. Paul's Chapel faces east, toward Broadway.
When practicing the line shoot via bow and arrow in France, the distance needed is clearly marked and Phillipe dances in celebration when the arrow surpasses it. Not long thereafter - with the group in New York - Phillipe has to pull a press conference ruse to get that same distance information. Furthermore, even if he hadn't already made his calculations back in France, it is as simple as measuring the distance at the base.