Several times, Mrs. Oster is called Mrs. Olson. Virginia Christine played Mrs. Olson in Folgers Coffee commercials.
When Dracula walks down a mine shaft with a torch, the light shines on the other side of the vampire.
At the end of the movie, Billy fires 7 shots at Count Dracula. All revolver's only hold a maximum of 6 bullets.
In the movie, Billy the Kid holsters his gun on the right side and fires right-handed. Henry McCarty, aka William Bonney, aka Billy the Kid, was left-handed.
The prop for Wolfsbane looks absolutely nothing like the real plant, which has a blue flower.
Dracula walks around in the daytime in several scenes. In Bram's Stoker's novel, the source of Dracula lore in the movies, sunlight restricts some of Dracula's supernatural powers, such as changing his physical form, but it doesn't harm him.
At the climax, Billy the Kid shoots Dracula. When that doesn't work, he throws the gun at Dracula. The prop apparently hit John Carradine's stunt double by surprise, right in the face, because he yelps in a way a bulletproof vampire would probably not.
When the bat flies down to the stagecoach, the prop operator controlling the descending mechanical bat is visible through the stagecoach windows.
Dracula is killed by a metal scalpel through the heart. Traditional vampire lore in the original book says Dracula must be killed by an iron stake. Most movies use wooden stakes, which are easier for actors to handle.
Dracula does not have a coffin to sleep in when he is picked up by the stagecoach. He never has one in the house after he moves in with Betty as her uncle. The mine where he takes Betty to make her his mate has a bed set-up, but vampires do not sleep in beds.