Costello running in fright in the radio station crashes through a glass partition, leaving a hole in his shape in the glass. Abbott, following, breaks away part of the glass to get through. Later, we see the hole in the partition in its original form.
When Bud and Lou first meet/search the two Police detectives Costello searches the Police Lt and feels his badge. He screams, yells out 'RING' and tricks the detective into answering the phone giving them time to escape. Abbott runs and exits the door with Costello close BEHIND him. In the very next scene from outside in the hallway the Camera shot shows Costello exiting the door in FRONT of Abbott.
When Juliet is telling Mervyn that he can buy her some ice cream after the radio broadcast but that she had to go take care of radio business, her voice is heard but her lips don't move. When she turns around after entering the studio, she says something, but it isn't heard.
When the knife is thrown into the Murder At Midnight sign, you can see it's going along a string.