Ok, go to the scene where the Muppets (Kermit, Fozzie, Animal and Pepe) go into Dr. Bunsen Honeydew's basement laboratory in order to find a way to save Gonzo. At the very start of this scene the characters are in the lab milling about when Bunsen asks them to gather around a table in the middle of the screen. As they move around the side of the table it's possible to see a puppeteer's heads pop up into the frame in the lower left corner of the screen.