Oldboy (2013)

Continuity mistake: During the ending, when Joe is seen burning one of the letters he had written Mia, when the camera cuts from a medium shot to the closeup of the letter burning, the handwriting on the envelope is slightly different, and the size/position of the fire has also changed.

Chaney: Shit, you might wanna think about what you're doing here.
Joe Doucett: I've been thinking about it for the last 20 years.

Trivia: At the beginning of the film, we see Joe buying a "rubber ducky" for his daughter from a female street vendor. The street vendor is wearing a set of "Angel Wings" on her back. This is a reference to the original Korean film, in which the lead character had bought his daughter a similar set of "Angel Wings" to wear.