Maestro Slatkin delves into how to convey the dramatic intensity the music calls for, and express the emotion underlying the dymanic, using the left hand and the rest of the body.
Sir John Barbirolli refused to take conducting pupils because he said that Conductors are born, not made. Well I had conducting lessons and I learn't what a conductor must do, but not how to do it. I had to find my own way of doing it and I think JB was right in that respect. You can learn the scores and practice beating time, but not how to deal with an orchestra. That most essential part of the job you have to figure out for yourself. Every maestro finds their own way.