When Kim makes a phone call just before getting kidnapped, she describes the man as having a beard. When Bryan hears this recording on the plane, it's changed to mustache, and again in a later scene when Bryan is listening to the recording it's beard.
When Amanda was taking a photo, the camera phone was held in the landscape position, but when Peter was taking the photo for them, he held it in the portrait position. Later, when Bryan was reviewing the photos, all the photos were in the landscape position, including the one supposedly taken by Peter.
When Bryan interrogates Marko, he removes his tie and loosens his collar. When he returns to the light switch, his tie has returned. Next time he hits the switch, the tie is missing.
When Bryan listens to the recording of his daughter on the airplane, the recording starts when his daughter says "They've got her", which would have been when his daughter was in the bathroom. Bryan originally started the recording after his daughter was under the bed in the bedroom, so the recording wouldn't include that part. It also would've recorded Bryan's voice, which was not on the recording.
When Bryan drives Kim to the airport, exterior shots show a Nissan Sentra. Interior shots show a BMW 7-Series, as evidenced by its unique seat and headrest design.
Bryan's diversion with the small walkie to avoid being caught when the French agents detect his cell phone location cannot work in the way depicted. First off, walkies usually are PTT, so either you can listen or you can talk, but to change from one mode to the other, you need to push a button.
Even if these walkies were to transmit and receive at the same time without hitting a PTT button though, Bryan would have to either dial or pick up the phone before he could start moving to his alternate location. That alternate on the other roof was too far for him to have reached it in the few seconds that pass between the start of the conversation and the first shot of static Bryan with his binoculars. But even if they had shown him on the move rather than observing, the French agents would have known he needed to stay in range of the low-power walkie for the trick to work, so he could not be more than a few dozen yards away.
When Bryan's friends come over for a barbecue, they are drinking Newcastle Brown Ale. However, as seen particularly with Sam's beer, the contents are too clear to be that particular brand of beer.
When Mills looks at the pictures on his daughter's cell phone chip, the computer says 'center' to center the image. In France, center would be spelled 'centre.'
The Impala failed to get smashed by the container, while all the other cars did. Also, the driver disappeared from inside the car, and in the next scene the Impala shows major damage despite the container not hitting it at all.
The police license plates have a single letter, which would make it a commercial plate rather than a police car plate. Police car plates in California only contain numbers.
Kim's map of Europe shows Czechoslovakia as one country. It split into the Czech Republic and Slovakia in 1993. However, she may have used an older map to plan her trip.
When Bryan listens to the mobile phone and the call ends, the audio sounds like a home phone cutting off, not a mobile. It's actually the sound of the phone being smashed. Later, the phone is discovered smashed.
Bryan never reloads his gun. He often takes the guns of people he has just killed, so reloading is not necessary.
When Bryan attacks the construction site, no one knows what he looks like, yet they know who to shoot. They could know each other by sight. Bryan, who is several inches taller, with much fairer skin and hair, stands out as someone who shouldn't be there.
Bryan is told that the kidnappers do business in "Yugoslavia," but no political entity has used that name since 2003. However, many people are not up on smaller countries' name changes, and use older names for countries out of habit. Since this movie was made only five years after then, it's a reasonable mistake to be made by someone not up on all international news.
When Bryan is chasing the sheik's barge along the Seine in his car, he appears to be traveling at high rate of speed alongside the barge. The barge would likely be traveling around 5 knots, about the speed of a light jog. The speed limit for boats on the Seine is 15 knots, (about 17 mph), so even if the boat could somehow travel at the maximum speed for the river (which would be impossible for a boat like that), it would still be at a crawl for a car.
When Peter jumps off the elevated road to escape Bryan, the semi-truck trailer Peter lands on clearly has a padded roof.
Bryan tells Jean-Claude that he has 96 hours to find his daughter, which was 16 hours ago, during a scene in full daylight. The kidnapping was shown to have taken place around 11 AM in Paris, 2:00 AM in Los Angeles; 16 hours later would have been 3 AM.
When Brian Mills is on the boat fighting the Sheik's assistant, Brian gets shot in his lower right side of his torso. Later when he see's his daughter off at the airport with his ex-wife, Brain Mills left arm is bandaged, but not his right side.
Bryan drives a 2004 Nissan Sentra, yet the interior of his car does not match that of a 2004-2006 Sentra.
When Mills is trying to get past St. Clair's bouncer to the auction, he shows the bouncer Pitrel's ID with his picture on it. The bouncer tells him his name is "not on the list." However, the ID card clearly shows the picture facing Mills rather than the bouncer, so presumably Pitrel's name would not be visible to the bouncer.
When Bryan has finished using the white SUV after the building site chase scene you can clearly see various bullet holes. These are in fact "Hardly Dangerous" bullet hole stickers that are often used in movies. This is clearly evident in the rear of the vehicle.
When the girls are in the apartment in France, they turn the music up loud so they do not hear Kim's mobile phone ring. When the camera pans over to her handbag, the phone is ringing, but "Silent" mode is selected.
When Kim first sees the new horse her stepfather has bought her for her birthday she says, "Oh, my God! Oh, my God!", her mouth movements and the first "Oh my God" don't quite match.
When Bryan goes to the girls' Paris apartment for the first time, he edges along a ledge on the outside of the building. An overhead shot reveals an obvious stunt double.
When Bryan is in the apartment of his friend the corrupt French policeman, they use the policeman's computer to check on the identity of St. Clair, the man who is auctioning Bryan's daughter. The computer is shown as having a QWERTY keyboard which is not the type used in France. It should be an AZERTY layout which is the type used in France.
When Bryan Mills tries to enter the apartment in Paris where his daughter was kidnapped, he uses a brown paper bag with groceries to appear a resident. These paper bags are typically American and not to be found in supermarkets in Paris, or most other parts of Europe.
Some men at the construction site wear hard hats that are not available or permitted in France. But seeing how the site is also the place for some VERY illegal trafficking, narcotics and prostitution crimes, it is not unlikely the men working there were also criminals and/or illegal immigrant workers who had brought their own equipment.
At LAX, Bryan discovers the map and drops his daughter off on the arrival level, even though her flight is departing for Paris. You can see they are on the lower level, which is the arrival level at LAX.
Bryan's only lead on Saint-Clair is the address 26 St Louis en l'Ile, Paris, obtained when Jean-Claude searches for him in the database. However, the mansion where the party is hosted is not the same building located at that address, as can be confirmed by a Google Maps Street-level search.
Granted Kim has been through enough trauma, but there is no scene following her rescue learning of her friend Amanda being dead. She is totally unacknowledged.
When Bryan shows up at the house on Rue Paradis as a senior official from the French police, he speaks English with an American accent. A gang of criminals like the Albanians would have been suspicious enough to keep him out rather than allow him to enter.
Bryan arrives at the house with the red door the morning after he raided and basically destroyed the operation at the mine, yet none of the people in the house seem to be aware anything happened. It seems reasonable they would be on high alert and especially cautious around a stranger. Even if they believed he was who he said he was, they should have questioned him about the events and asked what their money was buying them.
When Mr Mills visits the house on Rue Paradis, he appears to use a forged French ID to introduce himself as a policeman. But he speaks perfect northern Irish English throughout the scene. No one would have mistaken him for a Frenchman.
When Bryan shoots Jean-Claude's wife, the kids that were just put to bed don't scream at the noise.
When arriving at the house on Rue Paradis, not only does Bryan speak English with an American accent, but he also measures distance in miles.
Either of these mistakes are obvious indicators that he is not a French official.
The Albanian mob keeps close negotiations with the actual French authority, so they should easily recognize him as an impostor.
The attractive blonde who just arrived from Sweden for a vacation (whose kidnapping is interrupted by Bryan) has a Danish rather than Swedish flag on her luggage.
Bryan gives his daughter an international cell phone before her trip, but he doesn't give her a charger to keep it working.