Preview: Film Grammar.
People give meaning to shots depending on the content of previous and subsequent images. Lev Kuleshov's experiment from 1918 is famous. We see a man in close up. The next shot shows what the man is looking at. It is the corpse of a girl in a coffin. Then we cut back to the man again. Most people say that the man is looking sad and gloomy. That would be logical in such circumstances.
In other fragments, Kuleshov replaced the shot of the deceased girl by something else (food, a woman resting on the sofa, etc.). The face of the man remained the same. And every time the face triggered different emotions. So, viewers fill in the moods and emotions that fit the context.
In a TV interview, Alfred Hitchcock explained the principle in his own way. In the first clip we see an older gentleman (Hitchcock himself) giving a mother and child a tender look. In the second clip, the character is a dirty old man, staring at a girl in bikini. However, the shots of the man are exactly the same.