Robert De Niro's character, when discussing Sean Bean's character, mispronounces the town in England where the SAS HQ is. The actual English pronunciation is closer to "her'uh'f'uh'd", those "uh"s representing schwas and not Heer-ford as spoken by De Niro. However, there are many 'Herefords' in the USA (Texas, Arizona, California, and a few in New England) and many US Herefords are pronounced Sam's way, much as Americans often pronounce Edinburgh as Edin-Bro.
Vincent is supposed to be a mercenary or former intelligence agent with connections all around France to get whatever the team needs. Yet, during the initial briefing, he fails to recognize basic military terms.
Two Citroen XM's are used in the car chase in Nice: one old model (lateral Citroen logo) and one new (Citroen logo in the middle of the frontal part of the car). So throughout the chase, it is easy to see that they switch from one car to the other.
When the target vehicle is "400 m from the traffic light" just before Sam's team begins their assault, Gregor's computer displays its position as "LAT: 51 deg 52 MN 23 S, LG: 13 deg 5 MN 18 S". As the chase proceeds, at the point when "you should see them in 4 seconds", the computer again displays the position, and it's still "LAT: 51 deg 52 MN 23 S, LG: 13 deg 5 MN 18 S" even though the map has shifted.
Sam and Vincent are in the car, waiting for Gregor, Seamus and Deirdre to exit their safe house. Sam, in the near seat, has his side mirror angled so he can see straight behind the car. He makes mention to Vincent, who looks from the other side of the car. The mirror angle would mean Vincent could not see them from his position.
Gregor is driving a Jeep Cherokee with an automatic transmission when he picks up the man to do the transaction for the case. When he stops at the playground, he clearly puts the car into park. When he presses on the gas, the car lurches forward, even though it is still in park, and he is able to shoot the man in the head.
Deirdre is driving an early-'90s BMW during the final car chase; the car has stock 17" M "turbine" wheels. The wheel that Vincent is shown to shoot out is a standard 5 series wheel, and is not seen on the BMW at any point during the chase.
The car Deirdre drives in the final Paris car chase is an early-90s BMW 5-series. It is badged as M5, and has the correct wheels for this model. However in the tunnel scene, the dashboard shown is from a non-M 5 series, as all M models have red needles on the speedo etc, and this car has white needles.
As Witt is skating around the ice there is a shot of the crowd, completely packed. After that, there's a cut to Witt again, but now (only for a second) there is no one in the right side of the audience. The camera then pans left and for the rest of the shots the extras were obviously moved around to keep the appearance of a packed ice rink.
When Sam hands Larry the case he has an earpiece in his right ear. However when he notices the paint on his jacket and hand, the earpiece is missing. He then takes the case back and throws it and the earpiece is there again.
In the first chase while after the briefcase, the Audi sustains a fair amount of damage to the front of the car, including the headlamps being displaced. When the chase ends at the corner of the 3-way intersection, it shows an Audi with the front intact as it smashes into the front quarter of the Citroen. You can see clearly as the accident occurs that the driver-side headlamp is completely undamaged.
The Audi in the Nice car chase alternates between an A8 and a S8 (should be S8 as ordered by Larry earlier). S8 has silver mirrors and a three-spoke steering wheel. In some shots, the Audi has body colored mirrors and a four-spoke steering wheel that comes with the regular A8.
At the Roman coliseum at Arles, Vincent is surprised by the Russian, Sergi, who recognizes him from some past action. As Vincent replies 'Vienna' Sergi's gun arm is already straight but in the next scene it has changed position and is bent at the elbow.
When Gregor is standing in the pub looking for the two Russians near the arena, he looks through a camera to spot them. When we look through his lens, we first see them from below the viewpoint & far away. Then we see them again, through the lens above the viewpoint and closer, as if Gregor has changed positions and is now below the Russians. Yet we see that he has not changed locations in the following shot, he is still in the pub.
In Arles, when Sam, Vincent and Diedre are in the car looking for Gregor, Sam is told Gregor is "at the coliseum". In the next scene Gregor is still in the pub. Since his (presumably) CIA contacts are triangulating Gregor's cellphone and not monitoring his conversation, this is a simple editing error.
When Vincent is preparing to help Sam attend to his bullet wound, the outside of Sam's Kevlar vest surrounding the bullet hole is soaked with blood. When Vincent cuts the vest off, Sam's undershirt has very little blood on it.
In the car chase at Nice, Sam gets into the back of the brown Mercedes, behind Vincent. The next scene has him the passenger seat beside Vincent. While not impossible, it would be a rather quick switch in a fast moving vehicle to accomplish this.
During the second car chase when Larry forces the target car into the outdoor café, several diners and a waiter are knocked down by the cars and lay unmoving on the sidewalk. However, seconds later, after the bodyguard and man with the briefcase are killed, not a single diner is seen.
When Sam aims the LAW rocket launcher at the chase car on the mountain road, there is a car clearly visible behind Sam's Mercedes. A moment later when Sam fires the rocket, the car is nowhere in sight despite the scene being on a long straightaway.
When the shooting starts at the botched weapons exchange, a man on the left side of the arms dealer's car reacts to being shot at the same time Vincent is shooting the fat man. A moment later, as Vincent reloads, Sam pops out and shoots the same man on the left side of the car, who is now standing, ready to shoot.
Third and final car chase sequence. Right after the truck tips on its side and crushes several vehicles, we see a shot of it from the left side and crew and camera are clearly visible behind the guardrail on the far left.
(at around 1h 29 mins) During the final car chase, right after the police car flips over in the tunnel, a camera man and crane can be briefly seen on the left hand side behind behind a nook in the tunnel wall.
In the story a bullet goes through De Niro's bullet proof vest. He states it is because the bullet was sprayed with Teflon. Teflon will not cause a bullet to defeat a bulletproof vest. Teflon is used to protect and lube the barrel of a gun when firing steel core ammo. Steel core ammo may defeat a bullet proof vest but without lube it will wear out the barrel.
During the car chase, when the two cars swerve to avoid construction and drive along the dirt road, the camera switches between low tight shots of the fronts of the cars and you can see a cloud of dust from the camera truck in front of the lead vehicle.
During the car chase in Paris the hands on the steering wheel of the BMW during inside shots appear to be male hands (obviously the stunt driver). This especially obvious in a shot shortly after they have left the tunnel.