Continuity mistake: When everyone is running out of the theater, a woman with a red belt and yellow purse can be seen exiting with the other terrified patrons. A few seconds later, the exact same woman is seen running out of the theater again.
Revealing mistake: Joe is much too old to be in high school. He appears to be in his thirties (the actor playing him was 35 at the time).
Other mistake: After Van Helsing realises Dracula's coffin is in the cellar of Michael Gough's house, he hears a scream and runs to find the housekeeper Gerda overwrought and hysterical. He needs to find out where Dracula has just gone, and so he gives her a slap. It's hilarious how loud the sound of this is.
Continuity mistake: The interior of the ship is quite spacious, a central atrium on each level, with crew quarters and storage spaces opening off it. Yet, when the two officers take a space-walk down the length of the ship, it appears to have a diameter of less than 20 feet.
Factual error: This horror-fantasy film (a 1958 knockoff "The Mummy") was inspired by the faceless whole-body plaster casts taken from the volcanic ash of Pompeii, at the foot of Mt. Vesuvius. The running mistake in this movie is the assumption that the faceless bodies of Pompeii were 2000-year-old mummies preserved by volcanic ash and could, thus, be re-animated (by radiation, in this case). The fact is, the victims at Pompeii were originally encased in hot volcanic pumice and ash, and the corpses then disintegrated, leaving hollow "molds" of human bodies underground. It wasn't until the mid-19th Century that archaeologists first discovered the molds, filled them with plaster, then extracted the whole-body plaster casts for display. Since the faceless bodies of Pompeii are nothing but modern plaster casts, there would be nothing to re-animate, by radiation or any other improbable means.
Other mistake: Leonard Nimoy is incorrectly mentioned in the credits as 'Leonard Nemoy'.
Factual error: The film begins in 1860, but the majority takes place 20 years later, so 1880. When James Rankin obtains files on the Haymarket Strangler/Edward Styles case we are shown another box labelled with details about Jack the Ripper, who wasn't active until 1888.