"Once Upon a Time" is a delightful little example of hilarious slapstick humour, with a nice double act between the great Buster Keaton and Stanley Adams. I hadn't previously known that Keaton had ever appeared in a TZ episode, so this was a terrific surprise for me, in addition to that which I received when I realised that Adams was the actor who later played the trader Cyrano Jones in the "Star Trek" episode "The Trouble With Tribbles".
I found myself chuckling throughout this story, although the first incident that had me roaring was when Mulligan was being told off by the policeman during the first silent section of the story. I commented to a friend who was watching with me, "I bet he's saying, 'F-you, copper'". Sure enough, the next dialogue board to appear just read, "Censored!". xD Another thing I loved was the ridiculously silly Heath Robinson-esque (if you're American, think "Rube Goldberg") appearance of the time helmet itself. The thing even had sparklers on it! :P Priceless.