In this ten-minute video, Jim Henson, Frank Oz, and Michael Frith discuss some of the history and functions of muppets -- how they're put together, how simplicity leads to subtlety, and how to bring life to puppets. This is nerdier and not nearly as emotionally loaded as yesterday's post on Jim Henson’s Memorial Services.
It's unclear to me
when this was recorded, but I'm guessing it's the very late 1980's
-- as a commenter points out, it was apparently March 1, 1990. If anyone knows where this came from and when it was recorded, please post your info in the comments! NOTE: this video is cut off at the end; it's unclear how much more there is to this clip.
See also: Jim Henson Makes Muppets (Video, 1969) and rare footage of Muppeteers learning their craft in France. I would have included the latter video in this post, but the uploader has disabled embedding.