Christopher Reeve can be seen reading the "Superman" comic book Action Comics #506 (cover dated April 1980, which means it was in stores some four months earlier).
This episode is the first appearance of Rizzo the Rat. He began as a silent background character and grew into a prominent member of the Muppets troupe. Rizzo appears in a group of rats following Christopher around backstage. In addition, he mugs and reacts to practically every line of dialogue.
Christopher did not bring his iconic superhero costume when Miss Piggy talked him into finding it inside his dressing room's wardrobe. In reality, he was preserving it at the Warner Brothers studio in Burbank, California for the film production of Superman II (1980). Throughout this entire episode, he plays up references to his role of Clark Kent/Superman.
Rowlf the dog's feet make a rare appearance, sticking out from below the grand piano when he plays the intro to "Never Before, Never Again".