The Case of the Sleepwalker's Niece - S1-E2
Revealing mistake: The carpets in the sleepwalker's house looked like they're unfolded tarps. There are noticeable folds in the carpet that looked as if a folded cloth had been unfolded but the creases were still there.
The Case of the Drowning Duck - S1-E4
Other mistake: Marv Adams, doing magic tricks to entertain children, says he needs a duck for his next trick. A boy brings out a duck from the barn. We hear the duck quacking several times, but its beak never opens.
The Case of the Drowning Duck - S1-E4
Other mistake: The sign at the entrance to Clyde Waters' farm has the apostrophe in the wrong place. It says "Water's Dairy Farm."
The Case of the Silent Partner - S1-E6
Other mistake: A police officer sees a fire burning inside the home of Lola Florey and calls the fire department. The ground is dry. Stock footage shows three fire trucks speeding toward the scene, and the streets are wet.
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 Sun Bather's Diary - S1-E17
Character mistake: The reporter over the radio says Arlene Dowling is accused of murdering Frank Ballard, but the name of the murdered guy is George Ballard. Frank is her imprisoned father, Frank Dowling. (00:43:50)
The Case of the Haunted Husband - S1-E19
Character mistake: Doris Stephanak tells Perry that a car her friend is accused of stealing had "5,700 miles on the speedometer." She meant "odometer."
The Case of the Empty Tin - S1-E25
Other mistake: Elston Carr, hoping to locate a former business partner's daughter, has a notice printed in the newspaper. His address is 133 North Remuda Drive in Los Angeles. When his home is shown, the number painted on the curb is 3972.
The Case of the Desperate Daughter - S1-E27
Other mistake: When Perry telephones Edward Bannister, the father of a client, the view from Perry's office window shows that it is nighttime and rain is falling, but the wall clock in Bannister's home shows the time as 4:00.
The Case of the Hesitant Hostess - S1-E29
Factual error: Supposedly, heroin is being smuggled into the country in secret compartments in women's purses, but the quantity of heroin that could be concealed in such a way would be so small as to be very unprofitable for the smugglers.
The Case of the Screaming Woman - S1-E30
Visible crew/equipment: When Paul Drake opens the door to enter Perry Mason's office, the black-gloved hand of a crew member can be seen in the hallway.
The Case of the Substitute Face - S1-E32
Revealing mistake: While Perry and two other men are drinking brandy at a table onboard a ship, stock footage of a storm at sea is shown. To simulate the rocking motion of the ocean, the camera slowly tilts from side to side. This is obvious because the surface of the brandy in the glasses also tilts. If the ship were really rocking, the surface of the brandy would remain horizontal.
