This may have already been mentioned, but what I notice with the origins of Slapstick comedy is the physicality and how it plays a major factor. What you clearly see in "L'arroseur Arrose" is how the whole body plays an important role in slapstick comedy and continues to do so to this day. This film has served as a major template because physical comedy seems to be at the root of Slapstick like 'The Three Stooges', Chaplin films, and even in the more modern films (Mel Brooks films as examples).