Factual errors: Princess Ananka's mummy's death mask has closed eyes. In reality, the eyes of an ancient Egyptian mummy mask are wide open because the Egyptians wanted their dead to be able to see and hear in the afterlife.
Revealing mistakes: In the scene where the mummy breaks through an upper window and into Stephen Banning's padded cell at the asylum, a large smudge of the swamp mud that covers the mummy suddenly appears on the cloth wall, even before Christopher Lee slides down it, reflecting a prior take.