Continuity mistake: When Fletch goes to visit Calculus in his shack, he knocks on the window and sees Calculus sitting in a chair, wearing boots. The next shot, as Fletch is walking inside, Calculus is now wearing socks and no boots, despite never having left the seated position, nor having had any time to slide his feet out of the boots. (00:35:55)
Continuity mistake: When Tim gets stabbed, the killer's silhouette shows that he's holding his knife overhand. When he stabs Tim, he's holding the knife underhand.
Continuity mistake: In one scene, Tango sees a man looking in through the screen door, he jumps the man and rips open the screen. In the next scene, the screen is back to normal and covering the man's face. (01:11:02)
Continuity mistake: When Kurt gets into a fight orchestrated by Xian Chow at the bar, one guy smashes a glass against a table and holds it in his hand. In the very next shot of him, before Kurt kicks him, the glass is gone. (00:57:03)
Continuity mistake: During the classroom scene, the spelling of of Genghis Khan's name on the chalkboard changes from "Genghis Khan" to "Ghenghis Khan" between shots. (00:04:50)
Continuity mistake: When Redferne finds the page of the Grand Grimoire, he is holding it with his right hand. In the next shot, he is holding it with his left hand. (00:52:17)
Visible crew/equipment: Early in the movie Nancy visits Penelope. As she steps out of her car, the overhead microphone is visible in the front windscreen. (00:15:30)
Continuity mistake: In the scene where Belushi and Jerry Lee (the dog) enter the warehouse, Belushi askes everyone to stop what they are doing and even has the forklift driver lift him up so he can talk to them. Once he is done talking, he tells the lift driver to bring him down. The next few shots where they show Belushi walking to his car, if you look closely, you will see that the fork lift is back up in the air, but there were no sounds and there isn't another lift to be found. (00:25:05)
Continuity mistake: When Fuller falls to his death, the mannequin used as his stand-in gets decapitated on its way down. It even makes a loud noise. When Fuller lands, however, his head is still on his shoulders.
Revealing mistake: When Nathan walks into the classroom singing, the center sliding glass door on the back bookcase is closed in the initial overhead long shot, but in the tracking shots that door has been pushed to the side, so as not to see the reflection of the camera/crew as Nathan walks up the aisle following the camera. (01:42:15)