The Kuleshov Effect

Kuleshov edited together a short film in which a shot of the expressionless face of a man was alternated with various other shots (a plate of soup, a girl in a coffin, a woman on a divan). The film was shown to an audience who believed that the expression on the man's face was different each time he appeared, depending on whether he was "looking at" the plate of soup, the girl in the coffin, or the woman on the divan, showing an expression of hunger, grief or desire, respectively. The footage of the man was actually the same shot each time. 

This rule is key for our main thriller piece, and links into it as we now know the effect of cutaways and how they can be used effectively