Henry V famously opens with a "chorus"—a single actor who provides occasional narration—asking the audience to overlook the limitations of the Elizabethan stage: there will be no armies, no horses, nor any set to indicate whether one is in England or France. Rather, the audience itself must summon the various imaginary elements necessary to make the tale convincing. It's a clever device, with Shakespeare simultaneously acknowledging the labors of the actors, encouraging the audience to be engaged in the entertainment, and providing, through the narration, a vivid, thrilling description of the images he wants the viewer to have in mind.
How distant this is, seemingly, from the (most) popular entertainments of our day, the increasingly realistic dramas in video games and the CGI-dominated action movies such as The Avengers. Nothing, now, can be left to the imagination. Whereas a few decades ago, films still had to rely on an audience's forgiveness and willingness to accept what was clearly not real, now realism dominates, and so we've reached an age of cinematic literalism, in which fiction on film requires less and less of the viewer.
And yet. What of what's required of the actors? I recently saw, online, stills from various Avengers scenes, and what struck me is how little of what I saw on the film captured what the actors experienced. New York itself was digitally added to the film (as no actual filming took place there), and action scenes that appeared to be outdoors were instead shot on a huge sound stage, green screens backing every shot. I hadn't grasped the extent of what had been added post-production to the filming, and it made me realize that the actors, like the performers of the Elizabethan age, largely had to construct from their imaginations the scenes that audience would, later, directly behold. I think Scarlett Johansson was most effective in this, which is why director Whedon often went to her face for reaction shots: she excelled at looking completely undone by whatever she viewed, be it Banner's first transformation into the Hulk or hordes of aliens roaring from a hole in the sky. Despite the ingenuity of the people constructing a believable digital reality, were it not for the actors behaving as if they truly were these characters within these situations, the audience would not have fallen for the cinematic deceit. All the actors had to go on was what Shakespeare's troupe possessed: elaborate costumes, an entertaining script, and each other's shared imaginative enthusiasm.
The audience may no longer deserve exhortation and credit, as in Shakespeare's time, but we still rely on that "muse of fire" to enflame the actors, who must "ascend the brightest heaven of invention" to provide us with our play.