I was watching Sesame Street with my niece when I realized that the Muppet characters (portrayed by puppeteers) and the characters played by human actors do not seem to treat each other as different from each other in any fundamental way. Muppets are clearly sentient and possess civil rights, but does that mean that they really are human beings? I used to think that this was an absurd question, but the revelation a few years ago that Hello Kitty is actually a British schoolgirl and not a cat has made me rethink my biases.

In the world of Sesame Street, has there been any indication that Muppets are or are not biologically distinctive from humans? In other words, is the portrayal of Muppet characters using puppets rather than human actors simply an artistic technique (e.g. children like shows with puppets), or are we supposed to conclude that the likes of Grover, Elmo, et al. belong to a non-human species or civilization?