Because of the length of motion picture film, the film usually is wound around a core, with no other exposure protection aside from its packaging or the magazine itself when loaded. Therefore, the loading of motion picture film must be done in a dark room or light-tight changing bag by the clapper loader. As the loader cannot see what (s)he is doing, the loader must already be familiar with the magazine prior to loading a "hot" (in usage) roll and able to go through with the loading operations only on touch. When learning, usually a loader will start by practicing with unusably fogged rolls ("junk" or "gash" rolls) in light and then try with junk rolls in a changing bag after feeling competent enough.