Around fifty years ago — actually, not "around" fifty years ago; fifty years ago — I used to poach in the hallways of NBC Burbank and visit the sets where shows like The Dean Martin Show, The Tonight Show, Hollywood Squares or various Bob Hope Specials were rehearsing and/or taping. A fun place to be was the Laugh-In stage so I got to see Arte Johnson performing as his various characters.
In rehearsals, he used to mouth gibberish instead of the actual punch lines, the idea being to wait until tape was rolling to speak the real lines. That way, maybe actual crew and onlooker laughter might get on the air. (There was no studio audience there but there were an awful lot of folks like me hanging around on the set.)
Mr. Johnson's refusal to speak the actual dialogue sometimes frustrated his co-performers or directors and camerafolks who needed to know on what line to move the camera. But they all thought he was worth the trouble…because when he did do the lines in the script, he delivered them better than anyone else could have.
He would also deliver a lot of lines that weren't in the script. After he and Ruth Buzzi had taped a dozen Gladys/Tyrone skits, the director would just roll tape and they'd improvise a half-dozen more, including some of the best ones that you saw on your TV. He really was a very clever actor. No, I didn't know him but I saw enough of him to see how good he was. There were a dozen reasons that show was so memorable and he was several of that dozen. Here's a good obit that will tell you more.