Revealing mistake: When Natalie Portman's character is about to be executed, if you look at the wall behind the executioner, you can see a modern metal drainpipe.
Revealing mistake: While Frost is on the hotel balcony talking on the phone to Brennan, it is clear the phone receiver is not attached to anything.
Revealing mistake: When Tom Cruise and Bill Nighy go to see Tom Wilkinson for the first time there are 2 reverse shots from behind Tom and Bill - if you look you can see Tom's hand is still there - it has been digitally removed in all other shots.