When Mrs. Dimmock sneaks over to the neighbor's mailbox during the sand storm, she's wearing a long-sleeved coat and pink scarf. However, in the close-up shot of the mail being placed into the mailbox, her wrists are bare with no sign of a coat and the scarf (which can be seen blowing in the wind) is now green. Also, the hands are clearly those of a much younger body double and not those of actress Ruth Gordon.
In a scene where Mrs. Dimmock is talking with Claire about a stockbroker, Claire is having a cup of tea. When she finishes her tea she asks Mrs. Dimmock for another cup. Handing her just the cup, in the next scene she is seen to be holding both a cup and saucer. When Claire hears the dog Chloe bark, she jumps and almost drops the cup and tea spills out of the cup, meaning the cup was not empty when the tea was supposedly finished.
Towards the end of the movie, when Page is wearing the red wig, driving the 1960 Lincoln Continental with Gordon half-passed-out in the front seat, the interior shots show the car to be a 1961 or 1962 General Motors vehicle (discernable from the vent window and dashboard). Then it becomes a 1960 Lincoln again when they show the outside shots, and when the car goes into the lake. The Lincoln has a perfect rectangle vent window at a 90 degree angle; the GM car has a teardrop-shaped vent which is slanted back.
During the murder sequence that precedes the opening credits, Claire Marrable hits her housekeeper over the head with a rock while they are planting a tree, then shoves the woman into the hole. The older actress playing the housekeeper delivers a few lines in close-up just prior to her death and is clearly not the much-younger stunt double who falls into the hole moments later.
At around 37 mins when Mrs. Dimmock opens the door to sneak outside in the sand storm, the footage seems to be playing in reverse. As she's opening the door in front of her we can see dust from the storm billow up behind her and follow her out the door as she exits. Also, her movements appear slightly unnatural as a result of the reverse motion photography.
In the beginning when Claire Marrable is talking to her husband's lawyer, a mirror hangs on the wall. Right after she gets up and walks over to it, a crew member carrying a camera can be seen.
A microphone is visible at the sheriff's and Juan's feet in the police station.