Two identical or similar actors — for continuous shooting days or physically impossible scenes. Script coordination is critical; cut sequences must be planned.
Two actors—usually siblings or specifically cast—portray a single character over multiple shooting days or in scenes that one person cannot handle alone. The practice is older than one might think and only works if continuity and script coordination are perfect. Otherwise, chaotic moments occur on set that are impossible to salvage in the edit.
The classic reason: labor laws. A child can only shoot for four hours a day, and an adult in some jurisdictions no more than twelve. If you want a 16-hour montage with one character, you need two. The second reason—and it's underestimated—is physical impossibility. One person cannot be in two frames simultaneously, even with elaborate VFX. Here, producers save on expensive compositing tricks by simply using two people. The third reason is psychological: some performers cannot endure the intense physical strain. One twin performs actions, the other does close-ups. This works as long as the script notes document with micro-precision who is doing what in which shot.
The pitfalls are brutal. Small differences—a shifted mole, a different shoe size, a divergent posture—jump out at the editor. Costume and makeup must be identical, even the angle of jewelry, even the way hair falls. I’ve experienced shoots where one twin analyzed the other like a puppet. The script supervisor becomes a continuity machine—photographing every gesture, noting every glance. The editing preparation must show which twin plays which shot, otherwise the editing suite becomes a detective agency.
Practically, this means the director shoots a scene, then Twin A switches with Twin B without moving the camera. The lighting remains identical. A simple conversation with two characters costs double the shooting time because every reaction is shot twice. Some ADs solve this by reducing blocking intensity—longer takes instead of rapid cuts. That's smart. A skilled editor can weave twins in almost invisibly if the cut point is clever—cutting between profile and frontal, between action and reaction.