About 25 minutes in, a man in red trousers walks along the sidewalk. The same shot repeats about 10 minutes later.
At the beginning, in the shooting gallery, the first targets being winched backwards alternate between intact and bullet-ridden.
When Turk and Rooster are sitting in Dennehy's office, Turk's left collar is protruding outside of his jacket lapel. On the next close up shot, the collar is back in place.
When Turk and Rooster are in the church (near the beginning after the weapon has been planted) the harsh key light (sun ray from window) comes from stage right. When they cut to the close up it comes from stage left.
When the priest is shot in the confessional, his body is flung backwards. But when seen from outside the confessional, his body comes through the door face first.
When Karen is scared by Turk ringing her buzzer, she pulls her firearm out of her purse, cocks the hammer with her thumb, and aims it at the door. Karen carries a Glock 19 pistol (9mm). Glock pistols do not have exposed hammers, and cannot be thumb-cocked.
During the opening credits, Turk and Rooster fire H&K MP5 submachine guns, but then we see 5.56 rifle casings falling. The MP5 usually fires 9mm pistol rounds. They're rarely used by police, 10mm and .40SW variants exist.
When Rooster is sitting in the chair towards the end of the film he raises his Glock 19 towards Turk and the sound of a manual safety switch is heard. Glocks don't have a manual safety.
After they handcuff Spider to the vault door, Rooster puts his gun in his face, and you hear the gun cock. He's holding a Glock, which is striker fired and can only be cocked by pulling back the slide.
When Karen Corelli goes to her apartment, thinking she is being followed, you can see the shadow of the cameraman just before she steps up the first step leading to her door.
Club 404 is alternatively referred to as being at 184th Street and St. Nicholas Avenue, and being in Harlem. 184th and St. Nicholas is in Washington Heights, north of Harlem.
At the skateboarder's murder scene, a poetry card has been left, with the line, "Now someone must slap his whore." But when Turk recites the poetry out loud, he says, "Now someone else must slap his whore."