Anachronisms: Van Helsing says the little girl looks like a teddy bear. The movie takes place in 1888 and the term "teddy bear" was not coined until 1902.
Revealing mistakes: In Dracula's crypt, the now-aged vampire woman can be seen still breathing, even after she has supposedly been destroyed.
Revealing mistakes: About quarter of an hour into the film, immediately following the scene where Dracula attacks Harker and then carries the vampire woman out from the library, there is an establishing shot of the outside of Dracula's castle. It looks motionless, but on closer inspection, a dark figure can be seen rushing past the bushes around the entrance to the castle. The most probable explanation is that it is in fact the top of Dracula's carriage, and the shot was originally filmed for the scene a few minutes later when the carriage rushes past Van Helsing on his first trip to the castle. However, the carriage is so indistinguishable in long-shot, the editors obviously abandoned it and used it here instead.
Anachronisms: The vampire woman who attacks Harker is wearing 20th century high-heeled shoes.
Revealing mistakes: The supposedly dead Lucy reacts when Van Helsing and Arthur Holmwood looks into her coffin after she has been staked.
Continuity: The position of the bite marks on Jonathan Harker's neck changes considerably from the scene in which he is bitten, to the scene in which he inspects them with the mirror.
Continuity: The scar burned into Mina's palm by the cross changes its appearance completely when it is seen for a second time.
Continuity: At the start of the film, Jonathan Harker's journal narration establishes that it's May. Later, when Van Helsing and Holmwood ask the border official about the date Dracula's hearse would have crossed the frontier (within a week of the events that began the film) the date is given as December 1st.
Revealing mistakes: The actor's breath is visible in many interior shots, and very much so in several exterior shots.
Revealing mistakes: If you look closely as Van Helsing repels Lucy with a metallic cross in the cemetery, you can see in the reverse shot that Lucy is casting a reflection in that cross - a vampire no-no.