In order to create the feeling of the holiday season, Christmas decorations were kept in some streets of Bruges until the end of March. The town council made an official communication to the people of Bruges explaining the reason why.
The painting that occasions comment even from Ray is "The Last Judgment" by Hieronymous Bosch. Bosch-like symbolism recurs throughout the movie (the dwarf is one example), suggesting that Ray and Ken may indeed encounter their own Last Judgment - or that the waiting period in Bruges is akin to purgatory.
Except for the flashback, Ray wears a single outfit throughout the whole movie. While he does remove his jacket and unbutton his shirt, he has no other change of clothes. Ken, on the other hand, has several wardrobe changes.
When the characters visit Groeningemuseum they are shown viewing paintings "Death and the Miser" by Jan Provoost (ca. 1515), "The Flaying of Sisamnes" by Gerard David (1498), "The martyrdom of St George" by Unknown artist (1500-1510), and "The Last Judgment" by Hieronymus Bosch (1482).
Ken and Ray check into the hotel under the names "Cranham & Blakely", presumably after actors Kenneth Cranham and Colin Blakely who played two hit-men in a television adaptation of Harold Pinter's The Dumbwaiter, one of the film's major influences.
In a deleted scene, Ray and Ken are lying in their beds discussing Ray's murder of the priest and the little boy. Ray ponders over why he was sent to kill the priest, guessing it was likely pedophilia. Ken counters that Harry was behind a land-buying deal that the priest opposed. These two explanations are coincidentally two different motives that are suggested for the archbishop's murder in Primal Fear (1996).
Ken is never seen killing anyone on-screen (except himself) despite his profession as a hitman. Although given a gun to kill Ray on the orders of Harry over a botched hit, Ken fails to complete this task after preventing Ray's suicide attempt.