When Jessica ( Angela Lansbury )and Prof. Ames Caulfield ( Craig Stevens ) are checking into the hotel, the clerk tells them that she has two adjoining rooms in a private wing. Professor Caulfield thanks the clerk for being "flattering" which implies Professor Caulfield doesn't want an adjoining room being the gentleman he is. Professor Caufield telling Jessica to "come across the hall" emphasizes the propriety of their relationship.
The guy is singing, but he's singing so far away from the Mike there's no possible way that the Mike would be able to hear his voice.
A semi-automatic revolver features prominently in the episode. Although most revolvers are not semi-automatic, this is nevertheless not a goof as a small number of revolvers do feature semi-automatic designs including the rare Webley-Fosbery Self-Cocking Automatic Revolver featured in the episode.
In the bar, the man tells the singer/guitarist to stay away from his tramp sister, who was walking around serving drinks. He then insults the muso. The muso dives onto the insulting man while still wearing his guitar. Next shot is the two men fighting on the floor with no guitar in sight. Besides, no muso would risk damaging his guitar.
Early on, the blond lady who's tending tables goes to the bar and the bartender picks up a half-full jug of beer and fills it. Sacrilege. The jug has to be empty before the bartender fills it with fresh beer.