Jack Nicholson always gave high praise to everyone he worked with on the set, except one - the Raven. He said the Raven pooped on everyone, but especially liked to poop on him; he later said: "I would look down when the Raven flew off my shoulder, and it would be covered in poop....I hated that bird."
In casting his spells, Dr. Bedlo uses several Latin phrases: Veni vidi vici: I came, I saw, I conquered. De mortuis nil nisi bonum: Do not speak ill of the dead. Cave canem: Beware of the dog. Si vis pacem parabellum: If you want peace, prepare for war. Ceterum censio Carthaginem esse delendam: Furthermore, I believe that Carthage must be destroyed.
Among the humorous touches Richard Matheson worked into the screenplay were the Latin incantations used to cast spells, which any student of the language would recognize as the adages: "I came, I saw, I conquered"; "Beware of the dog"; "If you want peace, prepare for war"; etc.
Vincent Price later recalled about the final duel: "Boris hated being strung up in the air on those chairs. He was terribly crippled and we were both floating in the air on these wires. It wasn't a pleasant feeling! And I hated having that snake wrapped around my neck for two hours... I hate snakes".
Roger Corman said that although they kept closely to the structure and story script "we did more improvisation on that film than any of the others." The improvisation was in terms of dialogue and bits of business from the actors.
The events in the film take place circa 1506 based on two clues offered early on. Dr. Craven states that his father has been dead 20 years, and when they show the plate on the coffin the date of death is given as 1486. Therefore, 1486 + 20 = 1506.
In Spain hadn't a theatrical release until 1983, 20 years later. The film was only released -with 1 copy- at first in Madrid (November/83, Alphaville 3) and later in Barcelona (December/83, Casablanca 2), only projected in subtitled version. The dubbed version was for VHS premiere (1984).