This was my final project for school a couple years ago. The scene is a couple at home late one night when a stranger shows up at their door asking to use the phone. There was no script, no plot outline, and it was all shot in one uninterrupted take. The actor playing the stranger was given a back-story and a clear objective for the scene. The actors playing the couple were not even aware they would be joined by a third. They all reacted to the situation while we filmed with three cameras.