Starring: Raymond Burr, Barbara Hale, Ray Collins, William Hopper
The Case of the Moth-Eaten Mink - S1-E13
Plot hole: Perry Mason and Della Street are having dinner at a restaurant owned by Morey Allen. When waitress Dixie Dayton sees a diner who has been stalking her, she flees and is hit by a car. The next morning, Perry's incoming mail includes a retainer from Allen. His letter and check would not have arrived until the following day, at the earliest.
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.