The initial scene of the two casting directors was intended to be very dark, like an auditorium / stage. The camera rig prop that was used was the actual camera rig of the camera shooting the scene. In post production, the director felt the lighting was too dark and wanted it brightened a lot. In doing so, it could be clearly seen that there was indeed no camera sitting inside the camera rig which previously was covered in darkness.
A post matte image of darkened areas was superimposed to cover the missing camera in most shots, except for a few shots where Alison Kohlhardt's character creeps forward. In these shots you can clearly see the camera rig without any camera inside.
