Final answer:
The bus effect is a film technique used to create suspense and startle the audience.
Step-by-step explanation:
The subject being discussed in the question is an example of a film technique commonly known as the "bus effect." This technique is used to create suspense and startle the audience. The clip from the 1940s film showcases the woman's nervousness as she walks down a dark alley and the sudden appearance of the bus, accompanied by a loud hissing sound, causes the audience to scream.
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