Toward the end of the film, when Kim Sun-woo is walking down the corridor searching for his former boss, a guard sitting and reading a newspaper gets up to stop him. Kim Sun-woo shoots him but his gun is not pointed at the guard. Rather, it is clearly pointed at the wall where fake blood appears after the shot like a paint gun.
The goof items below may give away important plot points.
: When Sun-woo escapes his own clan, who are about to bury him alive for the second time, he smashes the rear left side of the car he's driving against a corner wall. A couple of shots after that, the car (shown from behind) is intact.