After Wilbur knocks the bundles containing their masquerade costumes out of Chick's arms and tries to dance with him, Chick say's "Come on, pick up these bundles and get dressed." Wilbur strides out of the frame without his bundle but he has it in his hand as he strides into the next shot.
Talbot , Wilbur and Chick arrive at the Masquerade Ball and you can plainly see it's already evening (with full moon in the sky), which means that Larry Talbot should have changed into the Wolfman already.
The placard that Wilbur reads to learn about Dracula in the museum is pristine in long shot, but creased and dented in close-up. The close-up was apparently shot after Wilbur bashed the sign against Dracula's coffin in the long shot.
When Dracula first appears, his hand grips the edge of the coffin twice.
It has been stated that vampires do not have a reflection in a mirror but Dr. Mornay sees Dracula's reflection in the mirror at around 53 minutes. and then the audience sees the reflection as well.
Larry Talbot says that when the full moon rises, he turns into a wolf. Larry Talbot turns into a wolf four times in four sequential nights. The moon is only full once during the cycle of the moon's phases. But werewolf movies frequently ignore strict scientific rules about the moon.
The title is sometimes considered incorrect as the characters never meet Dr. Frankenstein or his family, only his creation "The Monster", whom Wilbur calls "Frankie". However, it was explained in Bride of Frankenstein (1935) that the Monster is named Frankenstein after his creator.
When the Frankenstein monster starts to move on the lab table towards the end of the film the electrode on the right side of his neck starts to separate from his neck.
The first time Wilbur and Chick go down the stairs of the dungeon-cellar-dock, you can clearly see where the top of the "moldy brick" set ends, revealing smooth and clean studio walls.
In the House of Horrors, when the candle slides across the lid of the coffin as Wilbur reads the card, the wire that prevents the candle from sliding completely off the coffin can be seen.
As the monster begins to sit up in the crate in the house of horrors after being revived by Dracula, you can see the monster make-up separate between his right eye and brow.
While Dracula, in bat form, is floating outside the castle window looking in on Professor Stevens, the wire that holds the fake bat can be seen.
At the end of the movie when Frankenstein's monster is throwing barrels and crates at the boat, he throws more barrels than were on the dock to begin with.
The vampire bat that Wilbur swats at is a shadow and not an actual bat .
After Wilbur, Chick, and Joan Raymond arrive at the castle, Sandra enters the room and her reflection can be seen in a large mirror. She exclaims "Wilbur!" in surprise of added guests. However, in the reflection, her lips don't move.
When McDougal and his friend confront Wilbur and Chick on the pier towards the end of the film, Wilbur and Chick both say, "McDougal!" but neither Chick's or Wilbur's lips moves.
After Frankenstein gets off the table, Wilbur is heard screaming but his mouth is closed.
Chick tells Wilbur to untie the boat that they're in at a dock, while the Monster throws barrels at them from a pier. However, Chick's lips don't move as he talks to Wilbur.
Several times you hear Wilbur whistle but the sound either comes a few seconds before or a few seconds after , and several times when the two women are talking to each other , their lips don't always match up with what's being said .
Crewmember visible turning the secret door when Wilbur is running from the monsters in the cellar.
When Wilbur is on top of one of the House of Horror crates that is wobbling back and forth it can be seen that his feet inside of straps attached to the top of the crate to help him keep his balance and not fall off.
Shadow visible above the door that Larry Talbot exits from when Wilbur tries to return Talbot's suit case to him.
Bud Abbott and Lou Costello play characters named Chick and Wilbur in this film, but occasionally address each other as Bud and Lou. This was out of habit because these actors usually used their own names for their fictional personalities.
At 30.00 while Dr. Mornay examines the Monster on the other side of her island, Dracula asks if she's nervous. She drops her accent as she tells him, "This is risky business."
Charles Bradstreet is credited as Dr. Stevens, but his character is never once called "Dr. Stevens." He is always referred to as Professor Stevens.