Revealing mistake: When Dracula goes to grab the cell bars on the window to free Reinfeld, the bars are obviously not metal as they shake and have a slight bend to them.
Revealing mistake: As Mina is dancing with Dracula in the ball, we can see that in the mirror, she seems to be floating. Later on, as she is held by the arm and leg and spun around, we can see in the mirror that everything is in slow motion, even the orchestra conductor and a guest holding a fan.
Answer: A clip from Mutiny on the Bounty is used in the ship scene. I believe it's on deck before Renfield and Dracula are seen. The premature burial is the scene when Lucy's coffin is being carried on the moors.