Here's another version (different from this one) of Jack Benny and Mel Blanc doing the Sí/Sy routine. What's fascinating to me about this one is that it was obviously shot without a live audience. Benny, of course, controls the timing of the entire scene with Blanc responding to his cues. What Jack is doing in it is more or less replicating the timing of the bit as per previous times when they'd done it in front of actual, laughing human beings. He's leaving the proper intervals, presuming that whoever will add the laugh track later will follow his pacing and properly dial down the laughs. Benny even allows himself a slight smirk or two, like he's trying to prevent himself from breaking up, as he probably did when they performed this sketch on a live broadcast. And of course, Mel throughout is perfectly deadpan.
It's also a pretty good job of laugh-tracking, including the faint sound of recognition when Mel is revealed and the "audience" realizes it's this bit again…
