I don't think this was “on the set”, but rather part of some test footage to demonstrate that the Muppets could interact with the real world. Something to show the studio executives.

Jim Henson was one of the most playful, inspirational, fearless, positive, effortlessly imaginative people who has ever walked the earth. He helped us all see things a little differently; he changed the face of television, and helped us relate to each other better. I will never stop being grateful for the lessons I learned - and am still learning - from his creations.  When other kids were saying “I want to grow up and be a doctor / a vet / an astronaut”, at age five I was saying “I want to grow up and be an artist and work with Jim Henson”.  I guess one out of two ain't bad.

Awesome. When I was three years old, I used to watch The Muppet Movie every single night before I went to bed. I think I can still recite every single line from heart. “That's a myth! Myth! Myth!”
“Yeth?”

So awesome. The muppets were a great part of my childhood

Boo. Did not mean to click the WTF button. I adore this.

The day Jim Hensen died was one of the saddest days of my life. May he rest in peace. Sesame Street also gets credit for teaching me how to read at three years of age.