When Crystal comes down the stairs, she has a black silk handkerchief in her hand. She then kneels on the side of the sofa and starts talking to someone with the black handkerchief still in her hand. After the end of the talk, she tosses the black handkerchief away and it falls to the floor. When the camera cuts back to her, it's back in her hand again.
After Ferguson serves drinks to the two at the piano, he leaves with three drinks on the tray; when he subsequently opens the kitchen door and sets the tray down on the table, there are only two drinks on the tray.
While it is never explicitly stated, it can reasonably be assumed that Mrs. Dabney, like Mrs. Wetherby, is an American and thus her American accent is explainable; but no is reason given for why her eldest son speaks with a British accent and her youngest son speaks with an American accent. In one scene, Catherine even says that Ferguson (Raymond) could easily get a job in America as an English butler, which makes zero sense with Robert Taylor not even attempting to sound like an Englishman.
After Crystal and Ferguson close the front door on Dabney after the dinner party, a moving shadow of the boom microphone is visible to the upper right of the door.