In the scene with Jimmy and Kate on one of the trains, there's a dead guy (the train driver) lying on the floor. If you look closely you see he has a moustache. It was actually added on later using CGI so he wasn't confused with the previously killed security supervisor.
Advertising posters showing a bloody hand sliding down a London Underground train window were banned from the Underground as being in bad taste, even though scenes had been filmed with permission in disused stations on the Underground. Producer Julie Baines found this "highly amusing" and "a bit ludicrous", noting that the film is "not based on real events - if it is, we are all in trouble." The ban was later removed, although not in time for the film's British opening.
Near the end of the movie, Kate's hair is wet and she has a bloody nose. When she finds the platform again her hair is a lot dryer is and her nose is not bleeding.
Apparently not. The US Version of this British/German co-production has been cut. Several violent scenes were trimmed leading to a difference of approx. 20 seconds. A detailed comparison between both versions with pictures can be found here.