When the butler trips down the stairs, he throws the tray twice.
Virginia Bruce was dressed in black velvet and shot against a black background as part of the special-effects process of making her appear invisible. When the Invisible Woman is undressing in front of a startled Mr. Growley, her black velvet-clad arms are visible whenever they cross in front of her legs or torso.
When the Invisible Woman pours a dark colored wine into a glass, the resulting liquid in the glass is clear.
When Kitty is invisible in front of Mr. Growley, her shadow can be seen on the wall.
The professor's name is spelled two different ways: "Grawley" in the opening credits; "Growley" on his office door.
When Barrymore is sitting at his desk yelling "Housekeeper, Housekeeper", his lip movements do not match the soundtrack.