Just a quick couple of things on 39 Steps. Near the end of the show all four actors are on stage. The bad guy is about to shoot another of the characters. A hand parts the curtain and shoots the bad guy. The bad guy and the rest of the cast looks completely stunned. The bad guy then goes this was supposed to be a four actor play.
At one point they are on a train, one of the actors is playing a policeman looking for the main character. But he's also playing the train conductor. He switched hats back and forth as he plays each character. There's at least one sight gag in each scene. It was just a very very funny play.