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.
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 has an internal hammer, and can only be cocked by pulling back the slide.
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 Turk and Rooster leave the precinct house to see Charles Randall in prison they are driving a dark/black Ford Grand Marquis. En route they are seen driving on the bridge in a dark/black Lincoln Town Car.
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.
The goof items below may give away important plot points.
When Turk arrives at Spider's club to be set up by the other two detectives, a large sweat stain is in the middle of his sweat shirt. After that scene, it cuts to Rooster on the phone. When the scene cuts back to Spider and Turk a few seconds later, that sweat spot is nearly gone.
When Turk runs out of the lounge in Club 404, alarmed by Rooster shooting Spider, the gold plate on the plaque on the wall next to Turk's head is leaning forward, as it's been stuck into the bottom of the frame, on the outside of the glass. The camera cuts to Rooster holding a gun. When it cuts back to Turk, the plate is in glass of the plaque, a few inches above the bottom of the frame.