Gaffes

When the staff first appears in the study, a closeup of Hilda is shown, with Dr. Tart's card clearly exposed in her breasts, shortly before Tart hands her the card.

When the time gun fires during the detectives' first meeting with Phyllis, Inspector Winship's coat clearly has a bullet hole in the back. Later on in the movie, the hole is gone.

The acid in the tea is shown to be strong enough to dissolve a teaspoon, but when it spills onto Dr. Tart's fingers, he doesn't react to it.

When the detectives leave the Morley Manor, the trunk of the their car is open, and is still shown to be open in the dissolve cut, but in the final shot of the film, it is closed.

When Tart and Winship spy on Phyllis through the eyes of the painting, they slide pieces of wood away from the openings. When they finish, the sliding piece is gone from Tart's position.

Throughout the film, Dr. Tart attempts to send pigeons to deliver messages back to Scotland Yard, especially during the nighttime. In real life, pigeons can't see in the dark, so this would make no sense.

The film is called "The Private Eyes", but it is mentioned several times that the main characters work for Scotland Yard, meaning that they are not private detectives.

When the detectives pull up to the gas station, they notice that the price is "10 cents a gallon". While England does occasionally call them "cents", they mostly refer to it as "pence".

Jock is mentioned as having his whose tongue was cut out, yet he speaks in a slurred and garbled tone; someone whose tongue was removed wouldn't be able to talk at all.

When Winship and Tart are driving to/from the Morley Manor, modern vehicles are visible driving along in the background on Interstate 40, which runs through the Biltmore Estate (the filming location) in Asheville, North Carolina.

When the detectives find Justin in the secret passages, Dr. Tart's prop candle has a section visibly cut out, exposing the light bulb inside.

It's mentioned that Jock's tongue was cut out as punishment for trying to steal a ruby. But in the same scene, cotton can be seen in his mouth when he opens it, and his tongue is clearly visible.

After the old man stops filling the gas tank, the sound of the pump can still be heard going.

When Dr. Tart reads the line "By the way, you're standing in bull ca-ca," the dialogue is clearly dubbed in, and one can tell by watching his lips that Dr. Tart was saying "you're standing in bullsh..." (it's not clear whether he finished the swear or broke off).

When Winship and Tart first meet the staff, the boom is clearly in view when Tart starts his line, "Eeeny, meeny, miney mo... catch a killer by the..."

As Phyllis leads Winship and Tart up the staircase.