Here’s the opening few minutes of the Muppets appearance at the 1980 World Puppetry Festival.
I’ve never consciously realised this before, but the body language of each muppet is so well-defined. Kermit moves differently to Scooter, and Fozzie hold himself in a totally different way to Miss Piggy.
The event was staged in June of 1980, at the Kennedy Center in Washington. Some of it was filmed, and aired on PBS in a show called Here Come The Puppets!.
Here’s Statler and Waldorf advertising the festival.
And here’s a link to a full review of the whole festival.