The actors didn't know if they were shooting a scene or if they were just rehearsing. The camera was always shooting, providing some of the best and most authentic material for the final cut. It can be literally called "found-footage".
Nobody involved with the movie ever thought that it could find a way to a film festival, or even become a movie at all. The actors weren't aware of the footage or the full story. Many scenes were shot private, without the presence of any other actors, but only the director and lead character of the movie. Due to the fact that many scenes were constructed by 5 or 10 different ones, but had to look like one long shot, small cuts were made in between, showing weird angles of the room, or even objects. Those shots were relevant to the action, but the angle was always pretty bizarre (even from inside an oven or a pot). This technique made the movie to become very stressful and pretty intense, even during simple dialogue scenes.