Factual error: When Clint Eastwood first goes to the barber shop, the barber very deliberately sharpens his razor the wrong way, flipping the blade with its sharp edge against the strop - this would instantly dull the blade. No real barber would make this mistake, but it's a common movie error.
Revealing mistake: When the bad sheriff tries to run Buford Pusser over, he drives off the road and the car explodes for no reason. It's in the air when it explodes, there's no way it could have exploded without hitting the ground.
Continuity mistake: Right at the start of the movie, the dogs go though the bank's front door, which can only be opened from the outside, which means someone had to have opened the door for the dogs.
Continuity mistake: The hot knives that are set up in the King Lear scene towards the end of the film are sometimes smoking and sometimes not depending on the shot.
Continuity mistake: When Barbra Streisand meets Robert Redford on the street at the end of the film, the camera shoots her from behind and her coat collar is standing up. When the angle shifts to the front, her collar is neatly in place.
Continuity mistake: In one scene the actress is wearing a tight fitting sweater which clearly shows that she is wearing a bra. In the next shot she stands up to say she is off to have a shower, whips off her top and - you've guessed it - no bra!
Continuity mistake: Shortly before Sol's death, Thorn rushes into the suicide center and talks to him from the control room above. When Sol pleads Thorn to listen, there's interference on the intercom. Now watch the control panel: The earphone cable on the left side dangles back and forth each time the "speaking permitted" sign flashes on and off, blatantly revealing the cheap trick they used to make the display flashing - they simply toggled the "on" and "off" frames. (01:17:30)
Factual error: The records played in the fairground sequence "Sealed with a kiss" by Brian Hyland and "Runaway" by Del Shannon date from the early sixties, while this part of the film is set in 1959.
Continuity mistake: In the bedroom scene, Barbara Windor gets her dressing gown caught in the bed spring and has to take it off. When Sid James tries it on, he has no trouble removing it from the bed.
Audio problem: In the shop scene at Ginsberg and Cohen's, when Miles replies, "Something simple," he never opens his mouth to do so.
Continuity mistake: Trixie Delight's room number in the hotel is 235, but when Imogene and Addie go to Addie's hotel room, which is right next to Trixie's, the number on the door says 235, too.
Revealing mistake: At the beginning of the film, Stan reverses the bus into the manager's car. While the manager is under the bonnet looking at the engine, causing it to fall on him, you can see a rod with padding on it to stop the bonnet from hitting the manager. It is gone in the next scene.
Factual error: The kid is wearing a Texas Rangers baseball cap. The Rangers didn't come to Texas until 1972.
Factual error: The newly born foal is too dry and too steady on its legs. (00:22:25)
Continuity mistake: In the scene before the king and servant story, the people throw a lot of junk on one of the followers. If you look closely, you can see the accordion used in the scene before piled on him twice.
Continuity mistake: During entire scene with dancing king Herod and his men, shadows on the floor are at different angles from one shot to another. (01:16:15 - 01:19:30)
Revealing mistake: Right at the end when John is dying look at the texture of his blood. It is way too thin, almost like coloured water.
Other mistake: Dunnaway fires a warning shot next to her father to encourage him to leave the property. In the sequence just before he leaves she fires one shot and there are two dirt eruptions near his legs.
Continuity mistake: When Serpico finds three black men raping a girl in the park, one of them cuts the girls face slightly and the cut is very visible. The camera then cuts away then back and the cut and blood is gone. (00:10:25)
Visible crew/equipment: When Charles Bronson is chasing Paul Koslo through the flea market, the rooftop mounted camera set up can be seen atop the car.