In Macbeth: New Critical Essays (2008), edited by Nick Moschovakis, Michael David Fox has a fascinating piece entitled "Like a poor player: audience emotional response, nonrepresentational performance, and the staging of suffering in Macbeth" that brings out a very important aspect of the play: the concept of nonrepresentational performance, which to give a brief definition, is any aspect of the play that is designed to bring the audience into emotional or psychological contact with the actors as human beings, rather than as the characters that they're playing, and to therefore break through the theatre's "fourth wall" at certain points. This effect is achieved in the play's frequent use of asides (where the actors address the audience directly), its emphasis on the decision-making process during soliloquies, its use of sound effects such as the knocking at the gate and the alarum bell, its pervasive atmosphere of fear, its scenes involving the air-drawn dagger (where the audience's gaze is focused, along with the actor's, on an empty space) and the sleep-walking of Lady Macbeth. The essay helped to sharpen my response to each of the film versions that I've watched recently, and it reminded me once again of why criticism is of crucial importance in appreciating these multi-layered plays.