Years after Kuleshov created his experiment, director Alfred Hitchcock adapted the Kuleshov Effect into his own concept that he called “pure cinema,” which consisted of three shots:
Hitchcock’s addition of the reaction shot further clarifies for the audience what the character thinks or feels about what they just saw.
In a 1964 interview for the show Telescope, Hitchcock shared his insights into cinematic storytelling, ending with an example of pure cinema: Picture a close-up shot of Hitchcock squinting juxtaposed with a POV shot of a woman with a baby. His feelings toward this maternal pair are ambiguous until the reaction shot appears, showing his expression change to a smile. The audience concludes that he’s a kind and sympathetic man. Switch the POV shot out, however, so that Hitchcock is watching a woman in a bikini instead, and the audience shifts to perceive him as “a dirty old man.”
from MasterClass.com