This is the opening to The Unseen at A Red Orchid, and I highly recommend it. The production on the whole is powerfully acted and intimately, nimbly staged. But I can't stop thinking about those opening seconds.
When the audience enters the house the two actors are already on the set, each prisoner in his cell, trying to sleep. We know they are prison cells because 1) the walls are of big blocks of stone and the stage is split into two small spaces, 2) the beds are thin boards nailed to the walls, 3) the actors are dressed in rags and look gaunt and filthy, 4) we hear an insistent drip and maybe some distant machinery, 5) the only things in the cells with the actors are a bowl, a bucket, and a spoon. Notice anything missing? Bars: what may be the preeminent signifier of incarceration is absent, but we don't really mind. It could be simply because we are sufficiently accustomed to the "Fourth Wall" convention that it doesn't particularly matter what the wall is.
At any rate, already, some cognitive work has been necessary for the audience--before the play has even really started. We have worked to create the space suggested, and what is evidently permeable--an empty space--seems like an insurmountable obstacle. The play then begins with the sequence I just described (or something like it). It is, in some ways, a cinematic trick. Lights up and lights down to indicate the passage of time and create distinct tableaus is the theater's best approximation of jump cuts (Stoppard calls them 'Smash Cuts' in Rock 'n' Roll). But the miracle of this trick in the theater is that, unlike in a film, we have to negotiate the physical presence of the actor. So when the figure on the right disappears, we 'know' that the character (whose name we don't yet even know) is being interrogated or beaten or something terrible, but we don't know what happened to the actor. How did he disappear? In a film nothing could be more pedestrian, but on stage disappearing remains one of the most incredible tricks imaginable.
Brilliantly then, I think, this production simultaneously evokes and exceeds a cinematic commonplace toward a remarkable theatrical moment. We have created the bars ourselves, we have imprisoned the actors with the strength of our imaginations to such an extent that what is almost certainly true--that the actor escaped simply by walking out and down the steps--seems impossible, and our hearts freeze. When the actor reappears just as instantly, and we can see something terrible happened it's the same shock again, but now the play begins and we have no more time to think.