Goofs

In the opening scenes, the same woman in a red skirt and black top can be seen walking past Stanley's house (left to right) twice - firstly when Charles is collecting the newspaper and then when Charles and Stanley are leaving in the car.

During the opening credits whilst Charles is giving some background info, he puts on his waistcoat, does up the top and bottom buttons only, and immediately walks into the en-suite bathroom, and magically, the entire waistcoat is buttoned up.

As Stanley is hoisted by the jury following the verdict, the judge can be seen standing and stepping down from the bench. A moment later in a single shot, he is shown seated at the bench, waving his gavel triumphantly.

In the comic strip detailing the way in which he murdered his wife, Stanley includes a panel showing the purchase of a mannequin. The mannequin, however, is only used to represent his wife for the purpose of taking photos used in the drawing of his strip; it would obviously not be involved in an actual murder plot.

Jack Lemmon buys a powerful remote control unit that will control anything but surely not the mechanical crane that he uses it on; of course, "power" is not an important factor for any device, and on the crane there's no way for the remote to operate individual levers.