Plot hole: 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 after Andy manages to escape from the morgue.
Continuity mistake: At the cafe when Serafine says about Andy's friend coming along to "witness you score" Andy drops his coffee cup and you hear it breaking. When the condoms go onto the table the coffee cup is perfectly intact.
Factual error: The sirens on French ambulances have two distinct tones, not a single oscillating one.
Other mistake: Andy (as a wolf) obviously killed the dog in the cemetery because we hear the dog yelping, but in the morning when he's in human form the dog doesn't have teeth marks or a scratch on it, so how did it die?
Continuity mistake: When the werewolf jumps in front of the subway train, the woman in the purple top drops the same paper bag full of fruit twice. Once viewed from the side; once viewed head on.
Continuity mistake: 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.
Continuity mistake: After fighting the werewolves in the crypt, Andy goes back to the house and he has a cut on his right shoulder. However, when the werewolves turn up, he runs down the stairs and the cut has now disappeared.
Other mistake: When you first see the cop she has an English accent, the next time you see her it's a French accent.
Continuity mistake: Andy's glass jumps from his hand to the table after the toast on the train.
Factual error: 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.
Chosen answer: The Eiffel Tower has several elevators in use that they could have taken.
Bishop73