Oooops, I did it again!

Continuity can be a problem in movies, especially in epics like King Arthur:

During the battle at the end of the movie, the first wave of Saxon infantry is sent through the open door in Hadrian's Wall, and then it closes behind them. Mayhem ensues. All but one of the soldiers escapes after the Wodes fire arrows at them while the Knights ride them down. The single survivor staggers through the opening doors (which open just a crack, enough for the guy to slip through), and then stands there, and in that shot we see the doors behind him are now closed. An instant later, it cuts to the hillside where the Knights are standing on their horses looking down at the wall, and we see the doors both standing wide open. Scene cuts back, and we see they're closed again.