* ActingForTwo: Due to Glenn Strange having injured his ankle, Creator/LonChaneyJr played the Monster during the scene where he throws Sandra through the window.
* AllStarCast: In addition to Creator/AbbottAndCostello, it's the Who's Who of Franchise/UniversalHorror: Creator/BelaLugosi as {{Dracula}}, Glenn Strange as FrankensteinsMonster, Creator/LonChaneyJr as [[Film/TheWolfMan1941 The Wolf Man]], and [[spoiler:Creator/VincentPrice as The Invisible Man]]. Notably, this was the only other time Lugosi reprised his most famous role on screen.
* BannedInChina: The film was banned in Finland for years.
* {{Corpsing}}: The scene where Costello is unknowingly sitting on the Monster's lap had to be re-shot many times because Glenn Strange couldn't stop cracking up. Even in the finished version, you can see him starting to smile as he gets up to chase Costello. Outtakes showing Strange laughing have survived.
* DawsonCasting: Wilbur states that he is thirty in one scene, but Lou Costello was forty-two at the time.
* MoneyDearBoy: Lou Costello didn't want to make the movie, declaring, "No way I'll do that crap. My little girl could write something better than this." A $50,000 advance in salary and the signing of director Charles Barton convinced him otherwise.
* NoStuntDouble: Lenore Aubert did all of her own stunts and all her own screams. She wanted to do the stunt where she's carried and thrown through a skylight, but the director, Charles Barton, and the head of the studio, Robert Arthur, who were persuaded by Aubert to do all of her own stunts explained to her they were nervous and scared for her safety and while they took caution to not let Aubert get hurt in any way they could not let her be tossed through the window because the motion picture insurance company would never allow her to do it. The stuntwoman, Helen Thurston, when tossed through the sugar window fell on her right hip do to the fact that the cable wire she was attached to was given too much slack.
* TheOriginalDarrin: For the first time in seventeen years, Creator/BelaLugosi returns as Dracula, following two movies in which Creator/JohnCarradine played the role and another in which Wolf Man actor Creator/LonChaneyJr played him.
* TheOtherDarrin: Creator/BorisKarloff was reportedly approached about playing Frankenstein's Monster, but he declined, so instead Glenn Strange reprises his role as the Frankenstein Monster from ''Film/HouseOfFrankenstein'' and ''Film/HouseOfDracula''.
* PropRecycling: The ring Creator/BelaLugosi wears was reportedly the same one worn by Creator/JohnCarradine in ''Film/HouseOfFrankenstein''.
* RoleReprise:
** While he played other vampires, this is the only time that Creator/BelaLugosi explicitly recreated the role that he made famous in ''Film/Dracula1931''.
** Creator/LonChaneyJr filled in as the Monster for one scene, reprising his role from ''Film/TheGhostOfFrankenstein''.
* ThrowItIn: When the Monster punches through the door, Wilbur wasn't supposed to get hit. Lou was off his mark, meaning that Glenn Strange actually punched him very hard in the head. Amazingly, no one breaks character and Lou gives a hilariously dazed take to the camera.
* VoiceOnlyCameo: Creator/VincentPrice as [[spoiler: the Invisible Man at the end]].
* WhatCouldHaveBeen:
** Kharis the Mummy was originally going to be included in the cast of monsters, but that idea was eventually dropped. A Egyptian Sarcophagus appears in the movie as a possible nod to this.
** An early version of the script had the titular duo as workers on a ship transporting the dormant bodies of the monsters, who would've been revived when the boys spill their lunch, which just so happened to contain the [[AssPull newly-established]] combination of common kitchen ingredients that would do so, all over them.
** The scene where Dracula psychically lures Wilbur back into the castle was initally scripted to have Wilbur defiantly sit down on a rock and refuse to move, only for the rock take off into the castle with him along for the ride.
* WorkingTitle: The film was originally called ''The Brain of Frankenstein'', but it was decided that sounded too much like a straight horror film, and didn't capitalize enough on billing the famous comedy duo.
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