Andy is in hospital bed after Brad and Chris went looking for the suicide note, he supposedly sees "the mystery woman" in nurse garb walking down the hallway. When Andy gets out of bed to chase her, and is in the hallway, all the rooms windows are covered with frosted glass.
Andy's glass jumps from his hand to the table after the toast on the train.
Andy's hair changes beneath his bandage.
The wine levels in all three glasses constantly change.
On the train in the beginning, when Andy is looking at a map, the picture at the top of the map changes between shots. First, there's a little land and a lot of water at the top, then there's all land at the top.
When Andy bungee jumps off the Eiffel Tower, he hits his head on the rebound. If he had rebounded back from where he was shown, it would have smashed his skull to pieces and killed him instantly.
When Serafine transforms into a werewolf, her knees fold backwards to become the werewolf's hocks (the equivalent to the human ankle) and her upper leg bones bend forwards to become the werewolf's stifles (the equivalent to the human knee). However, humans and wolves have very similar leg structure, so there was no need for any of her joints to change, and she could have become a werewolf with just a lengthening of the bones from her ankles downwards. As it is, she will now have an extra joint in each leg.
All buses shown in the film are from Luxembourg; one even shows the logo "CFL" (Chemins de Fer Luxembourgeois).
The eyes of the werewolves in this movie have cat or fox-like vertical slit pupils. Wolves have round pupils.
The sirens on French ambulances have two distinct tones, not a single oscillating one.
When Andy is fighting Claude on the subway train, Claude is supposed to be naked after transforming back to human form again, but in several shots during the fight you can see that he is wearing pants.
This movie should have been called An American Werewolf in Luxembourg because, except a few scenes, all was shut in Luxembourg.
When Andy turns into a werewolf, he kills both Amy and Detective Benbou. Later in the morgue, Amy tells him because of this that she is forced to become his "rotting sidekick." If this is completely true, then Detective Benbou should also be following Andy around but he isn't seen for the rest of the movie as one of the undead.
When the werewolves are attacking everybody at the St. De Loup church, Chris begins to rock back and forth eventually causing the cross he's tied to to break and fall backwards. When the police arrive and people are escaping, Chris is seen running out of the church still tied to the cross. There would be no way for Chris to be able to get up and run since everybody was clearly trying to escape and nobody would stop to help him up.