When Daisy writes on the wall with lipstick, there is already text on it from previous takes.
When Wade visits Daisy after her breakdown, the way his coat drapes over his shoulders keeps changing between shots.
The scene in which Wood has a nervous breakdown while "looping" (re-recording) her own singing voice has the process backwards: By the 1930s, movie musicals had learned to pre-record their star's vocals, then have them lip-sync to the track on camera.
The copyright in the opening credits is shown as MCMXLV, which is 1945 and not 1965.
In the opening scene, Natalie Wood's character, Daisy Clover, leans back on what is supposed to look like a cement wall of graffiti. When she leans back, the wall leans with her to reveal it is made of fabric.
The wall in question is not concrete, it is actually a painted plywood wall of one of the many ramshackle buildings that lined the Santa Monica pier, so it makes perfect sense that it "gives" a little when Daisy leans back against it.
When Daisy finds her mother after her death, her mother's eyelids move.
The film is basically one big anachronism, since it features 1960s fashions, hairstyles, and music in a story supposedly set in the 1930s.
In the Swan Studios featurette that introduces Daisy the special effects that are presented were not possible in the 1930s, the song and orchestration are out of the 50s, and Daisy's costume is right out of 1960s Carnaby Street.
50's and 60's cars and trucks can be seen several times. Parked to the left of the pier. On the beach. On the pier itself. And in reflections and through windows.
When Wade opens a black glass door to get some glasses, a man is reflected in the door. He and Daisy are supposedly alone in the room.
The interior shots of the beach house are of a far larger structure than the size of the house seen from the exterior shots.