[math-fun] Panel puzzle

It's called a flexatube. Martin Gardner describged it in his 1961 book, "The Second Scientific American Book of Mathematical Puzzles & Diversions: A New Selection". Here's a picture and description: http://mathworld.wolfram.com/Flexatube.html I have often made these out of paper, putting red dots in the centers of the panels on one side and blue dots on the other. Tom