When Violet is struggling with a large ceramic pot stuck on her posterior, she reached for a fireplace tool to break it. When she does, the ashtray with the smoldering incense in front of the tool stand suddenly disappears between shots. It reappears closer to the arm of the couch in a following shot.
Around 51 minutes, when Violet (Beatrice Lillie) is playing the villain part in the play, the string can be seen used to pull off the mustache as she sneezes.
The end of the scene between Powell and Watson in the bank, Powell's cigarette is longer than it was at the beginning of the scene.