Continuity: When Sullivan is analysing the Providence corpses, the close-up shows both of his hands together, but on the wide shot one is near the corpse, and the other one close to his hip.

Continuity: After the beach scene, Costello is preaching young Sullivan on loaded guns. His cigarette disappears from his lips between shots.

Continuity: When Sullivan and his pal are watching the golden dome building from a bench, from a back shot his friend has his head faced straight, but from the front shot it's sideways.

Continuity: When Costello is getting his money in the diner, young Sullivan is first sitting next to some packages on the right of the screen , but a shot later, when he stands up holding a brown paper bag, he is seen sitting next to to an empty seat.

Continuity: After the football game, when Sullivan turns around to insult the other team, there's a guy with a light blue shirt that steps ahead of another one with a dark blue shirt. A second later their positions swap.

Continuity: In the scene after Queenan dies, when Sullivan picks up his phone, the number Sullivan calls Costigan in isn't the same as the one from which Costigan calls back, even though it's the same mobile (silver and blue vs. Costigan's red phone for Costello's gang). When Sullivan calls, the number begins with something like "617-854" and when he sees Costigan calling back, it's "617-177".

Continuity: In the scene when Billy is sitting inside Queenan's house, the glass of water is in his hand in one shot, disappears in the next and then returns.

Continuity: The position of Madolyn's spoon while eating the chocolate cake is not continuous in the front and back shots.

Continuity: When Costello tells the girl he has a hard-on, the position of her fingers on the blue book keep changing.

Factual error: In one of the opening scenes, where Martin Sheen and Mark Wahlberg's characters are first interviewing Leonardo DiCaprio and Matt Damon individually, Mark Wahlberg refers to himself as a "staff sergeant." However, the Massachusetts State Police has not had staff sergeants since 1992.

Revealing: When Costello's men drive off, after throwing Queenan off the top of the building, the undercover FBI are firing at the van. One back window is shot out, then in the next shot of the van the other window is shot out and then the same one is shot again so the one window is shot out twice in the same scene.

Continuity: When Dignam (Mark Wahlberg) reports the processor theft to the SIU detectives, he says 20 chips were stolen. When Fitzy opens the case at the sale, there are 66.

Continuity: While having dinner, from a side shot we see Sullivan's mouth chuckle. Frame later, from the front, he is serious and smiles half a second afterwards.

Continuity: During the opening scene at the diner, Jack Nicholson places a comic book in the grocery bag, and it is well below the top of the bag. In the next shot of the bag, the comic book is much higher in the bag, and in fact is almost rubbing the boy's cheek.

Continuity: Before French dies he starts to cough and there's suddenly less bullet holes in the windshield than in the previous shot.

Continuity: When Sullivan is questioning a bad guy, he sits down with a cell phone right in front of him. But later on, he reaches out to our left to grab it.

Continuity: When French is holding the bag with the hand he places a ring very close to Costello's cheek. A second later, without him having moved, the hand is at jaw level and farther away.

Continuity: Costello tells Costigan "your dad had his own code". Then Costigan turns his head and exhales some smoke, but the following frame shows his head in the opposite direction and the smoke is gone.

Continuity: Costigan enters the bar and points at a guy with a leather cap. In the background, a waiter is leaning on the bar, who then stands up and starts to walk. In the following close shot he is back in the previous place, leaning.

Continuity: After Costigan comes out of jail he visits an old lady. From a front shot she is slightly leaning, her left hand unseen. From a back shot the left hand is standing out over his shoulder with a burning cigarette. It should have been visible from the opposite shot at first.