Horror film effect (3)

I believe the answer is:

fog

'horror film effect' is the definition.
(I've seen this in another clue)

This is the entire clue.

(Other definitions for fog that I've seen before include "Bank restricting visibility" , "Heavy mist" , "Pea-souper" , "Confusion" , "Obscure" .)

I've seen this clue in the New York Times and the Penny Press.

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