When Susan Alexander Kane is doing the jigsaw puzzle by the fireplace, in the first wide shot it's clear that the puzzle is almost complete, but in the subsequent close-up the puzzle has hardly been started.
In the newsreel, the announcer states how a defaulting boarder had left the deed to a supposedly worthless mine (the Colorado Lode) to Mary Kane in 1868, then begins his next sentence, "Fifty-seven years later, before a Congressional committee," as the film cuts to an old newsreel of Thatcher testifying before the committee. Fifty-seven years after 1868 would be 1925. As "talking" pictures were at best still in the experimental stage and in any case not in use in 1925, it would not be realistic that the newsreel of Thatcher testifying before Congress would have sound. Similarly, the sequence immediately following Thatcher's testimony, stated by the announcer as "that same month in Union Square", depicting the radical speaker denouncing Kane, would also not have had sound.
When Mr. Thatcher has Mrs. Kane sign the contract at Mrs. Kane's Boarding House, Mrs. Kane goes over the closed window and opens it. In the first shot, the window could only be raised to the height of Mrs. Kane's shoulders, but in the second, it is above her head.
When Kane's second wife is recounting the moment she left him, the suitcase that is open on the bed has frills on the inside. When we hear the butler continue the story, Kane walks back towards the suitcase to close it, and the frills are gone.
The jigsaw puzzle that Susan is putting together changes considerably between the shot where Kane walks into the large room and asks her what she's doing and the next cut, where Kane is standing in front of the large fireplace. The amount of puzzle that she has completed increases greatly between the 2 shots.
The first time we see the backstage preparations before Susan sings, the shadow of the curtain rising has a completely straight bottom edge. The second time we see this scenario, this time from behind Susan, as the curtain rises, the bottom of the curtain is adorned with a series of prominent curves.
The large sofa (with a table behind) moves between the shot where Kane sits down in the armchair (while Susan does another puzzle), and the cut to Kane's POV. The sofa and table move almost into the line of sight between Kane and Susan between shots.
When Kane returns from Europe, he enters the Inquirer news room and rushes towards the camera, which dollies back. At this point, and when he subsequently leaves, the dolly track is visible on the floor.
The Russian newspaper lists Charles's first initial as C. In Russian, that letter is pronounced S. There is another letter in Russian, that looks like an upside-down lowercase h, that is pronounced CH. Either that letter, or K for the Russian form Karl, should have been used as his first initial.
In the beginning, Kane says, "Rosebud." The nurse enters the room after the word is spoken. The shooting script only mentions Kane and the nurse being in the room. However, within the movie itself Raymond the butler tells the reporter that he had heard Kane say "Rosebud" after the fight with Susan as well as just before he drops the snow globe, implying that what the viewer is shown in that scene is from Raymond's P.O.V.
During the picnic scene towards the end, Welles had to shoot against a back-projection because a location shoot was too costly and time-consuming. The stock footage used for the exterior was taken from King Kong, hence on closer inspection the four birds that fly by are in fact very definite pterodactyls. RKO told Welles to take the pterodactyls out of the shot, but he liked them, and decided to keep them.
When Kane hovers over Jed Leland's unconscious form after Susan's horrible opera debut, the paper in the typewriter had a thumb mark in exactly the same place where Kane will grab it out of the typewriter a few seconds afterwards. Evidently they shot this scene at least once before.
The long dolly shot from outside the Kane house in Colorado and all the way back inside through two rooms, ending on the far side of a table, could not have been achieved with the table in place and, instead, the table had to be moved into position once the camera was past. It's an almost perfect illusion except that the hat on the table is still wobbling slightly (from the sudden movement) by the time it comes into shot.
After Kane's mother signs the contract for Thatcher, she stands up and seems to walk through the table on her way back to the window. This is due to the table being moved in order to create a continuous tracking shot from the front of the set (where the table was) to the back (window).
At the moment Mr. Bernstein meets the old newspaper publisher Mr. Carter and shakes his hand you can see that the ceiling is just cloth, and a wire and part of a mic boom is visible through the material.
When Susan is reading the news about her debut, the front page is displayed prominently. While the first paragraph or so of each story is indeed about her performance, the rest of the news stories are obviously not (with the exception of Jed Leland's negative review).
In the newsreel sequence, a gazette in Spanish is shown, announcing Kane's death. The newspaper's name is "El Correspendencia" but that name simply makes no sense for Spanish speakers. The closest match to this would be "La Correspondencia" because most of the words that end with an "A" are meant to reflect a female gender and the correct article is "La", not "El". However, that literally means "The Mail" and this is just a generic name which is fairly related to news media. Also, the words "Murió" in the header, as well as the "Xanadú" in the article's text are misspelled because they lack the accent marks on the last vowels. Another mistake is "Destinguido editor" instead of "Distinguido editor" can be read below the article's title. Finally, the title would never be written as such in Spanish (you can read "Madrid" in the paper): you wouldn't say "El Sr. Kane se murió" but rather "El Sr. Kane ha muerto". It might be a "Heart of Darkness" reference, with the intention that it be translated as "Mr. Kane, he dead."
When the photographer at the party snaps the photograph of the former-Chronicle-now-Inquirer reporters, he is standing much too close to capture them all inside of the frame. At that distance (about 3 feet) he would only be able to capture about 3-4 of the men sitting there.