The Case of the Laughing Lady - S9-E1
Continuity mistake: Professor Toby is shown in the background as someone in the audience is highlighted, but is supposed to be on the witness stand and appears there in the next instant.
Perry Mason (1957)
1 continuity mistake in season 9
Starring: Raymond Burr, Barbara Hale, Ray Collins, William Hopper
The Case of the Sausalito Sunrise - S9-E19
Revealing mistake: Secretary Della Street answers the telephone in Perry's office and speaks briefly with the owner of an art gallery. She presses the "hold" button, then hands the receiver to Perry and says, "It's Mr. Clune." Perry and Mr. Clune have a lengthy phone conversation, even though Della never released the "hold" button.
Hamilton Burger: Incompetent, irrelevant, and immaterial.