Stupid trivia: Harvey had a thumbtack in his hand, and when he was tempted to laugh, he’d squeeze it. OBVIOUSLY it didn’t work. But early on in this skit you can see him start to laugh, and see it change to a pained expression. NOW you know why.
When a Freeper posted this a couple years ago, I watched it for the first time. I have no idea how Tim Conway could even rehearse this. Absolutely incredible.