Deliberate mistake: The priest that Ray kills doesn't stagger out of the confessional booth toward the little boy until he's already been shot twice, yet when Ray sees the boy he accidentally shot, he is still kneeling in the prayer position and therefore did not move or react whatsoever to the first few gunshots only a few feet away.
In Bruges (2008)
1 deliberate mistake - chronological order
Starring: Ralph Fiennes, Colin Farrell, Brendan Gleeson, Elizabeth Berrington
Continuity mistake: When the barman pulls Ken a fresh pint, the pint is placed on the bar and the glass is not entirely full. The camera changes angle and the glass is now full.
Ray: Why didn't you wave hello to me today when I waved hello to you today?
Jimmy: I was on a very strong horse tranquilizer today; Wasn't waving hello to anybody. Except... Maybe to a horse.