I used to think that Barkley and Alice were regular puppets as opposed to full-body characters, since they weren't big. And even after learning they were indeed full-body Muppets, I thought they were both played by midgets. I was surprised when I first learned that Barkley's performers had to hold onto stilts. The 40th anniversary books says that the reader might be surprised to know that only one person is inside Barkley, given his size... But I wasn't surprised to know that.
When I first saw how the Gorgs were performed in The Secrets of the Muppets, I thought that all full-body Muppets were performed that way. I pretty much figured out how Snuffy worked after seeing the credits for Follow That Bird and saw two people listed. I first figured how Big Bird is performed after seeing The World of Jim Henson, which showed an image of a sketch showing how the bird was supposed to work.
After seeing A Muppet Family Christmas, I thought it was semi-normal for people to sleep on hangers (though I never tried it). I noticed that Gonzo and Animal were hanging differently, so when Floyd said "That's the only way Animal ever sleeps", I thought he was referring to the way Animal was hung, thinking that Gonzo was hanging the "correct" way and Animal the "wrong" way.