The song "Never Before, Never Again" was originally sung by a professional singer dubbing in for Frank Oz (as Miss Piggy), but the producers did not think her rendition was as funny as Frank Oz's version.
In a 2004 interview, John Landis revealed that he was the puppeteer for Grover during the final sequence, as Frank Oz was busy operating Miss Piggy. Landis also noted that Tim Burton was also among the many puppeteers in the finale.
The illusion of Fozzie driving the Studebaker was achieved by having a midget drive the car via remote control from the trunk, using a television monitor to guide his steering. The puppeteers would lay on the seat or floor and couldn't see a thing. The first time they tested it, the television monitor went on the blink, and the driver had to be talked through the scene by an assistant director on a walkie-talkie ("A little to the right, now, to the left...hold it...").
This was the last movie to feature famed ventriloquist Edgar Bergen and his wooden sidekick, Charlie McCarthy; Bergen died shortly after his scene was shot in 1978. It held particular meaning for Jim Henson, who cited, on many occasions, how Bergen and McCarthy were the major reasons he took an interest in puppetry. A dedication to Bergen is included in the end credits.
Jim Henson was determined to use the larger budget of a feature film to push the technological limits and capabilities of puppetry. One of the most difficult feats (and one that appears deceptively easy on-screen) was making Kermit ride a bicycle.
Orson Welles plays a studio executive named Lew Lord who draws up a standard rich-and-famous contract for The Muppets - a reference to real-life producer Sir Lew Grade (later Lord Grade). When Jim Henson was trying to find a producer to make The Muppet Show (1976) happen, no American network understood or was interested in the concept, Grade recognized Henson's vision and made the show possible.