"Let it also be borne
in mind that Scrooge had not bestowed one thought on Marley, since
his last mention of his seven-years’ dead partner that afternoon. And
then let any man explain to me, if he can, how it happened that
Scrooge, having his key in the lock of the door, saw in the knocker,
without its undergoing any intermediate process of change—not a
knocker, but Marley’s face.
Marley’s face. It was not in impenetrable shadow as the other
objects in the yard were, but had a dismal light about it, like a bad
lobster in a dark cellar. It was not angry or ferocious, but looked at
Scrooge as Marley used to look: with ghostly spectacles turned up on
its ghostly forehead" (Charles Dickens page 16).
Many of the population still believed in superstition (even though Scrooge didn't), and it hadn't yet left the society.