Stumbled on this earlier today.  Fun and frivolity abound!

http://io9.com/5921611/jim-henson-improvising-on-the-set-of-the-muppet-movie-was-pure-magic/gallery/2

Thank you very much for sharing. Pity that I didn't get much of the words. And I don't get why none of the cars driving by crashed. I think I would have crashed mine, seeing Sweetums on a field!

I watched this last night, it's doing the rounds of the internet - brilliant stuff and a demonstration of how good improv can be.