After Gerald Pyncheon (Vincent Price) discovers the burial vault, he has the lid to the vault almost back in position, and after a quick cutaway, he's shown with the lid standing up once again about to place it.
As the mansion is beginning to implode, Jonathan Maulle (Richard Denning) attempts to remove the slab from the burial vault, but it's thicker than the one Gerald Pyncheon (Vincent Price) placed on it.
'House of 7 Gables' - After the painting above the mantle bleeds it changes to another painting. At the end when the house is destroyed the original portrait reappears.
At 1:58 when Gerald is being strangled by the skeletal hand, he is in the chair which had a blood stain in the upper right hand corner. However, there is no blood stain visible now.
When Alice exits the room to check who opened the door, the light is bright around her and then hallway is shown. When screen goes back to her, the light is much darker around her.
Dr. Carl Heidegger is shown to be able to tell the mineral content of water just by looking at it under a microscope. In reality he would use chemical analysis and spectroscopy to determine such things.
At 1:21 when the watch floats down to the table, it lands with the chain on top of the watch. However, in the close-up the chain is now on the table.
Considering the amount of fat Carl had on him, it is doubtful he could have been killed with one stab in the stomach.
As Alex and Sylvia finish their conversation while Carl is upstairs getting her wedding gown, they are both standing, and Alex is holding Sylvia by her upper arms. When Carl comes down the stairs with the gown, Sylvia stands up from sitting in the chair (she was standing just a minute ago) and Alex is holding a drink that wasn't there before.
During the segment The House of the Seven Gable at 1hr 56 min, the missing skeletal arm of Mathew Maul is revealed. The wires that hold the bones and joints together are clearly visible.
Sylvia is clearly breathing while dead and in the coffin.
If Gerald really did struck his sister with a pickaxe, the wound would have been much bigger.
Obvious fake pillars in front of the house because they roll so easily when they fall.
The staples shown in the 1859 calendar would not have been invented until 1866.
In the 'Dr. Heidegger's Experiment' segment of the film, while Vincent Price and Mari Blanchard are having a conversation in front of the portrait of Blanchard's character, the shadow of a boom microphone can clearly be seen moving back and forth above and between the shadows of Price and Blanchard.