The first time Martha Winthrop brings up a glass of milk to Phyllis Allenby, the glass is half full as she walks up the stairs to the bedroom, but after she opens the door and enters the room, the glass is nearly full to the top.
When Martha Winthrop falls down the stairs and is stabbed with the knife, there is no blood visible when she raises herself up.
Although their characters are supposed to be English, Don Porter and June Lockhart make no effort to conceal their American accents in the film.
When Phyllis and Carol sit down to talk, the shadow of the boom mic is visible on the wall behind them.