Night of the Demon (British version - somewhat longer) deals with magic in both the sense of prestidigitation and in the sense used by anthropologists for supernatural manipulation of non personified power. Magic, which involves sleight of hand "tricks" that leads the audience to believe something other than what actually happened (or perhaps to wonder how the "trick" was done). In many ways the camera work plays with magical practices such as misdirection. These are apparent in the opening scene.
The film is a salute to Val Lewton and the films he made in the 1940's which Lewton felt dealt more with terror than horror. Another salute to those films was made by Robert Wise called The Haunting which is sometimes described as Lewton film on steroids.
Lewton's desire NOT to show transformations and leave much of the material in the viewer's head rather than on the screen was a contrast to the films of Universal Studios, whose films were full of such things.
Notice the difference between "shock" and "suspence" and how they are made meaningful in the film. Are shocking things really supernatural? What about the things that happen after a suspenseful build up?
For a closer look at the film, clik on Night/Curse of the Demon