Continuity mistake: Near the end, Mick and the other two bad guys are chasing Sondra to the carousel. Mick shatters the glass door with his rifle on the right. after a chase,she runs to the same glass doors only to shatter the left door this time, while the right door is now intact.
Visible crew/equipment: At one point Clint Eastwood is out in the woods practising his shooting with his new .44 auto-mag pistol. While he's doing this, a car pulls up and a black male begins to get out with a shotgun. (We later learn that this is his partner). As the man with the shotgun is opening his door, if you look at the reflection in the car window, you can clearly see the reflection of a man with a camera and another man standing next to him.
Revealing mistake: In two scenes, at the pistol range to get used to his Automag pistol and in the hotel room when Harry has lost his model 29, S&W and is getting his Automag pistol. In both scenes, Harry picks up the Automag pistol, then a magazine and pushes the magazine into the pistol butt. Both times the magazine has no cartridges in it. You can see the spring through the witness slot on the side of the magazine. The pistol won't fire if there are no cartridges in the magazine.
Plot hole: During the last gunfight, Harry puts 3 or 4 rounds from his Auto-Mag into Mick, who then falls through the roof of the carousel and impales himself on the unicorn horn. Although it was demonstrated that those .44 rounds would penetrate 1/8 inch steel, none of them made it through Mick's body, as there was an absence of exit wounds in his back.
Factual error: In the final gun battle at the end of the film, Harry shoots the last bad guy so he falls off a high spot on the roller coaster and through the roof, into the carousel building. Yet as the credits roll, there is an aerial shot and you can see the carousel building at the left of the screen, with no hole in the roof. Also, the carousel building and the roller coaster are about 200 yards apart.
Other mistake: When Harry gets to his vacation spot he is greeted by a dog. A few seconds later the dog is seen lifting his leg to pee, showing his dog is a male. Later on in the film after he returns home after the main killer has killed the second victim, the dog is scratching at the door. If you pause the movie at this moment you notice the dog has a sagging belly with nipple's just like a female dog after delivering puppies.
Continuity mistake: Meathead, the dog, changes from a female to a male dog several times throughout the film.
Continuity mistake: On Harry's way to and from the fish market, it changes from day to night too fast.