Buster Keaton used a hand double in the shot where he writes, to avoid showing his right hand with the missing index fingertip.
Buster Keaton's stunts are tame in this movie, compared to his usual rugged and demanding stunt work, because he was recovering from a broken ankle.
In this short Buster Keaton took credit for every part and job, including editor, director, writer, cameraman etc. This was a reference to 'Thomas Ince''s (the "inventor" of the Western) reputation for doing this.
The multiple Busters on screen together were created in the camera, using a special lens with shutters to film only a portion of the scene at a time. Buster would perform one part, then the cameraman would crank the film back and open another shutter to film another part. A banjo player with a metronome helped Keaton to perform precisely at the right time for each take.