When Rizzo comes in and whispers something to Kermit during "The Elves and the Shoemaker", it is obviously not Rizzo's voice. This is because Steve Whitmire was already performing Kermit in this scene. The Muppets typically use this method of substitution, then dub in the correct voice later, but it appears this instance was overlooked. The voice is almost certainly that of Dave Goelz.