Editing is often proclaimed an invisible art. A smooth experience shaped from rough resources, through countless iterations, with the component parts as inconspicuous as possible in the final product. The audience is guided through the story by a hidden hand, unaware of the techniques employed in the edit to do so. Editors sometimes joke that awards in their field should, but never will, be given to disastrously directed, shot and acted films, somehow dragged kicking and screaming into mediocrity by a talented editor. Occasionally, though, a film finds success with very visible editing, in which immersion via the commonly accepted language of traditional editing is abandoned in favour of something particularly expressive.

Adam McKay's Oscar-winning Wall Street crash comedy The Big Short is a case in point. The visible editing here is a bedlam of bold, brash characters, fourth-wall breaking celebrity cameos and to-camera narration, and a hyperactive blend of infomercials, cable news and music videos.

Editor Hank Corwin, who previously worked with Oliver Stone and a similar visible style on Natural Born Killers, utilises freneticism to convey Wall Street anxiety in the lead-up to the 2008 crash. In addition to the excitement of the general pace, each character grouping of the ensemble was cut in a different manner - an "editorial signature", as Corwin describes it. This approach differentiated the personalities and their emotional states, with an aim for an experiential rather than observational audience experience. Steve Carell's eruptive Mark Baum received aggressive cuts designed to disturb the eye, while Christian Bale's cerebral Michael Burry was conveyed through a more rhythmic, detail-orientated style. With these various atypical techniques going against the grain of the audience's normative expectations and engagement, Corwin knew he had to balance them out with immersion in other ways. He found an interesting means of balance in footage of the actors when they were unaware they were the focus of the camera. Providing Corwin with this essential footage, more than perhaps a prescriptive form of cinematography would, was Director of Photography Barry Ackroyd's verite-aesthetic camerawork, which freed the camera to react to the improvisational performances.

Hank Corwin explained his use of this technique in a December 2015 interview for Slate:

"It could be a moment where they think the camera's on someone else, or someone else is acting, and they're waiting, just being themselves. And for just a brief moment you get to see real reality. I find, so many times, actors--even the most skilled actors--they subtly slip into the roles. And I think it helps if you can mix their real personas in with their characters, because I just think it makes a much more realistic, accessible performance."

The philosophy of authenticity behind Corwin's technique is similar to that of realist directors, such as Ken Loach. Loach is renowned for his use of non-professionals and the emotional manipulation of these actors in order to bring a sense of reality to the contrivance of filmmaking. He explains the mixing of professional actors with his newly discovered talent as a way of creating his own balance. On occasion, he would go so far as to practise a form of Method cruelty in order to produce real emotions. In his 1969 film Kes, he convinced first-time actor David Bradley that one of the kestrels he'd grown attached to during filming would have to be killed for the ending. This inevitably produced the emotional response Loach desired in the poor child. The 2006 Canadian indie Half Nelson combined a Loachian use of non-professional actors with the loose verite cinematography seen in The Big Short. To find her balance, editor Anne Boden used real behaviour found in 'tops and tails' (the footage before and after the action of a shot), and shots sneaked in during set-ups, to intercut with the fabricated scenes. Regardless of the method, the aim is the same; finding natural moments to offset the artificiality in the filming process.

Naturalistic acting can often be almost indistinguishably close to the real thing, but can never truly be natural. The camera and crew have an observer effect on the actors, and all the unreality of the set, process and performance can spill into the final film. It's part of the editor's role to stem that tide. The subtle change in an actor's body language when they don't feel watched by the ever-present eye of the camera can subconsciously affect the audience's suspension of disbelief. Almost imperceptibly slight movements in the actor's face, called microexpressions, reveal emotion to the audience in mostly unconscious ways, through a process rather distressingly named 'emotional leakage'. This is the evolutionary lie detector we are all born with, and its manipulation is one of the keys to emotional authenticity that was the goal of the realist acting schools of Strasberg and Stanislavski. Credibility in front of the camera and details in body language can be controlled through training, but the observer effect can still materialise in ways neither the actor or audience are conscious of. An actor ensconced in their role and the scene, though, without the added pressure of knowing they are the focus of the camera, can more readily provide these details as if naturally occurring - perhaps simply because they are.

When an editor is offered that perfect moment of an actor emoting without pretence, whether through that actor's effort or a natural reaction, it can be a keystone in crafting a sense of reality. Corwin's work on The Big Short shows that the emotive power of visible editing techniques doesn't have to lead to any collapse of immersion when threaded with these moments of potent authenticity.