The above famous Russian roulette scene was dominated by what is called shot/ reverse shot. This scene consisted of the above 5 camera setups and a few cutaways. While CAM#4 is called the reverse shot of CAM#2, CAM#2 is called the reverse shot of CAM#4. The same goes for CAM#3 and CAM#5.

How do you get precise shot/ reverse shot like the mirror image of themselves?

All you have to do is (refer to the diagram above):

1) Use the same focal length lens. (Magnification)

2) Maintain the same distance between camera and the object. (Distance)

3) Keep the same angle between imaginary line and camera axis. (Angle)

As the tension between them gets intensified, 1)the size gets bigger, 2)the distance to the object gets closer, 3)the camera goes around their front. Somewhere along the way, the objects turn out to be the subjects for us.  We realize we have been absorbed in the diegesis. These factors (Magnification, Distance and Angle) serve as 3faders to control the subject-object relationship.

Family Plot (Alfred Hitchcock, 1976)

Ostensibly a jeweler and a customer, they are actually kidnappers. When they pretend to bargain, camera is set perpendicular to the imaginary line and shows their profiles. When they whisper to avoid other customers from overhearing, camera axis almost overlaps the imaginary line and camera displays their frontal faces. Hitchcock put us alternately into the most objective viewpoint and the most subjective one(Point-of-view shot). 

The alternating repetition of shot and reverse shot tells there exists an imaginary line out there. In the case of The Deer Hunter, it is their friendship which is invisible but which we wanna see. Shot/ reverse shot implies an imaginary line between them, that is, their relationship. In fact, only an invisible line can connect irrelevant shots to each other. Just take a look at the next video.

In this case, Imaginary line is the path of the ball. Every shot is elaborately filmed and edited so that sequential shots have the relation of shot/ reverse shot through the path of the ball. Otherwise they will fall into pieces.

L.A. Confidential (Curtis Hanson, 1997)

This shot/ reverse shot wasn't filmed by two simultaneous cameras. It's obvious because both shots were filmed against the light. If they were filmed simultaneously, either one's back would be too bright to pay attention to the other's face. That is due to creating a halo around her blonde hair. But lighting isn't the only reason shot/ reverse shot is filmed by a single camera. Another reason is changing position. For instance, if there is an irremovable obstacle in the background, you can avoid it by shifting the position as the diagrams show below.

Whether parallel or pivot shift, the thing is to keep the relative positional relation. It's all about how the object distinguishes itself from the background. When the background rises to the surface, the object decomposes. The imaginary line to guarantee the connection between juxtaposed shots also dissolves. Therefore, if you wanna depict the relationship, what you should show is an invisible imaginary line.