Unfortunately, the Leica's take-up spool needs a long tapering tongue of film, which users must wedge under a spring clip on the spool's barrel before manually wrapping a few turns of film around it.
In their bid to simplify loading 35mm film, Kodak, Fuji and other photographic firms squared off the 35mm roll's lead-in tab so a modern SLR's motor-driven loading mechanism could grab the film's sprocket holes and wind it automatically onto the take-up spool.