Other mistake: After the third homicide, everyone gathers around the statuettes of the ten little Indians. Small problem, though. There are eleven little Indians. (00:42:20)
Other mistake: While reading a book in the Hall of Records, Jake notices some names are pasted in. One of the pasted in names is spelled "Clarence Speer." The name comes up again as Jake Gittes and Evelyn Mulwray are driving away from the orchards. The name is spelled in the subtitles "Clarence Speer" and Jake pronounces it "Clarence Speer." Later Jake and Evelyn are reviewing the Mar Vista Rest Home Activities Board. Here the name is spelled "Clarence Speers." (01:07:35 - 01:17:25)
Other mistake: In the original version of the film there's a mistake in the opening credits where Colin Blakely's name is misspelled as Colin Blankey.