After stopping the PAGANs at Caesar's Mansion, Jerry Caesar walks up to Joe Friday and offers to repay him by giving Friday a lifetime subscription to "Bait, Dollies, and Field and Cream". Yet when the PAGANs are torching the magazine warehouse at the beginning of the film, there is a large sign on the side of the warehouse that shows the magazine titles in Caesar's line as "Bait, Field and Cream, and Cable Girls". "Dollies" isn't mentioned.
When Pep rescues Friday from the PAGANs at the Observatory, Joe picks up a Beretta 9mm pistol. But when he turns to shoot back at the hoods before hopping onto Strebeck's bike, Joe is firing what appears to be a 1911-style .45 auto.
When Joe and Pep are chasing the reverend at the end of the film, there is a scene in which Joe drives a police car on the wrong side of a expressway tunnel. When the shot pans to Pep covering is face, you can see, looking over his shoulder, that they are driving past store fronts. However, when the camera pans back out, they are still in the tunnel.
Sgt. Friday is suppose to be a by-the-book "never break the rules" cop, yet in the opening scene as he is pulling up to the police station Friday parks in front of a fire hydrant and gets out. Parking in front of a hydrant is still illegal in California.
When Joe, Pep, and Granny Mundy sit down at the Brown Derby they are at a booth with Granny sitting in a chair on the side. When Connie notices the Reverend (and all subsequent shots) they are now at a table, all in chairs.
In the scene where the LAPD Ramming Tank is cutting a swath through the milk factory, if you look closely in the very back of the warehouse, you'll see two men in yellow jumpsuits and gas masks standing and watching the tank cut across a line of pipes. When Joe and Pep emerge from the tank, they are wearing yellow jumpsuits and gas masks. The two men in the background observing the action shot may or may not be Dan Akyroyd and Tom Hanks watching the stuntmen driving the tank in the scene and waiting for their turn to shoot their scene of them emerging from the tank.
In the scene after Joe, Connie, Pep, and Joe's Grandmother leave The Brown Derby separately, Joe is seen taking Connie to an overlook that is under the Hollywood sign. Though the approximate size is about right (around 300-310 feet long), there is no place to park below the sign.
When Joe Friday and Pep get Captain Gannon and the Commissioner to go to the site of the PAGAN event, Friday's narration indicates they met at 5:45 a.m. on a date in April. However, it is full daylight when they arrive. While sunrise is as early as 5:41 a.m. in Los Angeles, that does not occur until June whereas the average sunrise time in April is about 6:10.
After diving into the snake pit to save the Virgin Connie Swails, Pep takes a handful of pills from his pocket and pours them into the snake's mouth. Capsules of this nature are water-soluble for obvious reasons and after they'd spent several minutes underwater in Pep's pocket they would have dissolved into a goop. The pills that Pep gives the snake are clearly bone dry.
At the end of the movie the police car is shown driving down Century Blvd making you think they are heading to LAX. In the next scene you see jet radio is set to 119.3 which is the frequency for Van Nuys airport Tower - about 15 miles away.
When Joe and Connie are kidnapped by Emil, they are in Joe's police issue Yugo. When Joe is rescued by Pep at the observatory, they escape the PAGAN goons on Pep's motorcycle. At Jerry Caesar's mansion, Pep tells Joe to go home, to which we later see Joe driving down the road in a beat up Mustang. However, since he obviously got to Caesar's mansion riding on Pep's bike, there is no explanation as to why or how Joe got a hold of a Mustang to drive home.
During the raid on the drug facility/milk processing plant, the liquid that spews from the pipes and drums turns out to be milk. However, it is obviously not milk, not even skim, as milk would be a more solid color of white, as opposed to the nearly transparently white colored water that we see.
Pep Streebeck is watching television using the Seiko brand "TV Watch". He is clearly not using headphones; but the Seiko "TV Watch" has no external speaker and requires the headphones to hear any audio. He is also not using the television's antenna. Therefore, not only should there be no sound coming from the watch, there should also be no reception either.
After the shoot-out at the Caesar mansion, as Pep and Friday drive away a marble statue can be seen with very neat bullet holes through it. Due to the structure of marble (or any stone), bullets would not simply punch a smooth-edged hole in it, they would break chunks off. That the hole is black shows that the statue is also hollow and obviously a prop.