Revealing mistake: In several of the sanatorium scenes, you can see large pieces of cardboard attached to the lamps to affect the lighting.
Revealing mistake: When Renfield walks up to the front door of the castle, he is in a court yard where the only light comes from torches. But the light is enough to make him throw a clear shadow on the wall, and the shadow never flickers as it would in torch light.
Answer: Pretty sure this qualifies as a mistake, just like the llamas in Troy. Armadillos only live in the Americas. Later on, they have opossums too! So the story about not wanting to show rats could very well be true. Nevetheless, if this isn't a mistake, I don't know what is.
Spiny Norman