After several takes that never looked quite right, Faye Dunaway got annoyed and told Jack Nicholson to actually slap her. He did and felt very guilty for it, despite it being Dunaway's decision. The shot made it into the movie.

At the time of filming, Jack Nicholson had just embarked on his longstanding relationship with Anjelica Huston. This made his scenes with her father, John Huston, rather uncomfortable, especially as the only time Anjelica was on set was the day they were filming the scene where Noah Cross interrogates Nicholson's character with "Mr. Gittes...do you sleep with my daughter?"

Roman Polanski said that in staying true to the tradition of Raymond Chandler's detective stories, he shot the whole movie from the perspective of the main character.

Jack Nicholson (Jake Gittes) is present in every scene of the film.

Screenwriter Robert Towne was originally offered $125,000 to write a screenplay for The Great Gatsby (1974), but Towne felt he couldn't do better than theF. Scott Fitzgerald novel and accepted $25,000 to write his own story, "Chinatown," instead.

Continuity

In the orange grove scene, Gittes's car has its right front tire shot and deflated, yet it is not deflated when the car hits the tree.

When Jake gets in a fight with the owners of the farmland, one of the lenses of his sunglasses pops out. However, in the last shot, he's lying down with the sunglasses intact.

Gittes lights a cigarette while waiting to see Yelburton for the second time. Entering his office, he takes a puff, but when they shake hands, the cigarette is gone.

When the knife man (Roman Polanski) sticks his switchblade up the nostril of Jake Gittes, the sharp side of the blade is positioned inwards, not outwards, and the cut is made with the dull side of the knife. The following reverse angle shows the man holding the knife with the sharp edge up.

When Cross and Gittes are lunching, the close-up of Jake's plate does not match, with the fish, potatoes, and lemon wedge being in completely different positions.



Factual errors

Among the items in Ida Sessions's pocketbook, which Gittes rummages through, is a social security card with a typewritten account number. Social Security cards have always had a red stamped account number, never a number added with a typewriter.

It is an urban myth that Los Angeles is a desert and has no water supply of its own. Los Angeles is in fact a Mediterranean climate and does have water, just not enough to support the needs of the population, hence the need for outside water sources and the tight control of it.

When Jake is photographing Mulwray and the girl from the rooftop, the composited reflection in the camera lens is not reversed.



Incorrectly regarded as goofs

When Gittes takes photos from the rooftop of Mulwray and a young woman, the scene cuts away to a shot in front of Gittes, where his 35mm camera captures Mulwray embracing the woman on the terrace below. However, the image in Gittes's camera should reflect an upside down image of the couple. According to the interview with Roman Polanski on the DVD, he deliberately chose to show the couple right-side up to make it easier for the audience. He also said that "now" (in 1999) he would have shown it as upside down, as it would be in reality.

When Gittes visits the orange grove and crashes into the tree, you can see that a steel plate has been placed around the tree to protect it.

When Gittes gets drenched by the water, he's completely immersed in it. Then moments later his suit is fairly dry looking as though he had only been splashed.



Revealing mistakes

They're in a drought and heat, yet when Jake enters the orange grove, fully ripe oranges can be seen. Oranges ripen in winter and are all picked before spring.

At 1:10:13, as Gittes' car is backing up, the car hits the camera rig and the camera shakes.

When Gittes first drives up to the Mulwray's home, it's supposed to be lunchtime, but the long shadows indicate this scene was shot in the early morning or very late afternoon.

When Jake arrives at Ida Sessions's apartment at 848-1/2 E. Kensington in Echo Park, the trees in front of the building shift back and forth while the building does not, indicating a poorly executed overlay.

When Jake Gittes is about to enter the orange grove, he encounters a sign that says, "Keep out, no trepassing." Instead of saying "trespassing," the sign says "trepassing."



Miscellaneous

When Jake goes to the county records office, he's told the records he's looking for are in Row 23, Section C. He walks down Row 24.



Anachronisms

During the "Mulvihill! What are you doing here?" scene, the elevator call buttons are modern, automatic-elevator type with lights. In the 1930s, elevator call buttons were generally black and had no lights.

As Jake and Evelyn leave the nursing home, several cars from the 1970s can be seen passing on the road outside.

When Gittes awakens and sits up on the ranch house porch after being being knocked unconscious in the Trident Ranch orange grove location, a circa-1974 refrigerator can be seen through the window behind him.

When Mrs. Mulwray drives away from the Coroner's office, a siren is heard in the background. The siren is a modern electronic one. In the 1930s, they only had mechanical sirens, which have a different sound.

Police cars use the higher-pitched style of siren commonly heard from the 1960s onward, not the lower-pitched style characteristic of the 1930s.



Audio/visual unsynchronized

The tires squealing when Gittes pulls into the driveway of Katherine's house.



Crew or equipment visible

Early during Jake and Evelyn's post-coital cigarette, a mechanical noise is heard in the room - presumably the result of an incautious crew member.

Reflected in the glass behind Gittes while he signs the contract with Mrs. Mulwray.

When Gittes and Evelyn are leaving the Mar Vista Inn rest home, there are brown plastic photographic gels visible over each of the glass panels of the front windows and the front doors. However, when Jake kicks Mulvihill and runs outside, and the camera films through the windows, the gels are gone, and the windows are plain clear glass.



Errors in geography

The clerk in the Hall of Records says some of the plot maps for the northwest San Fernando Valley are in Ventura county. The county line is well to the west in the surrounding hills.

When Gittes and Evelyn Mulwray are arguing after lunch in the Biltmore Hotel's limousine lane location (while the valet fetches her Packard), the camera is facing west towards the 1926 Checkers Hotel at 535 S. Grand Ave. However, the camera is angled in a way that reveals a completely incongruous 1967, forty-two-story AT&T building (address is 611 West Sixth St) just to the south of the fifteen-story Checkers Hotel.

Duffy calls to inform Gittes that he's tracked Mulwray to 'Glendale and Douglas'. Glendale and Douglas do not intersect but run roughly parallel.



Boom mic visible

When Jake is in the barbershop and has an argument with a banker, he gets out of his chair to get in the banker's face. When he returns to his chair, you can clearly see a reflection of a boom mic in the window in the background.



Character error

During lunch with Jake, Noah responds to the Mariachi band and company by waving at them. However there was no one in the group were waving at them or even looking at them.