One thing that's always fascinated me with the Chan films is the evolving technology on display - from the "tetrogene" in "Murder Over New York" to the "first generation 'fax' machine" (pictures by wire on two synchronized machines on different coasts) in "At The Opera" (?) to the music "repeater" and use of UV light in 1936's "Secret" (the underwater filming in the beginning of that film is in itself somewhat of a technological marvel for the time) and so on.

Not to mention Charlie taking the "Hindenburg" on the last leg of his trip to see #1 in the 1936 Olympics.....