People and birds have two legs, ""animals"" four, insects six, spiders eight, and ""snakes and snails and wiggly worms"" have none. To demonstrate these truths the Kesslers show children running, jumping, and dancing on their legs, then show several kinds of birds, farm animals, and so on, using theirs. The words of the text might be those of a resolute nursery school teacher determined to keep the class moving: ""Two legs./ Legs that walk./ Legs that hop./ Legs that jump./ Legs that run--/ FAST!/On your mark./ Get set./ GO!/ Legs that dance./ Legs go marching/ down the street./ One, two, One, two./ Marching, marching./ We are marching,/ Marching, marching,/ down the street."" The pictures are correspondingly bright and beaming, and all that's missing are the piano chords thumping away. With a real teacher directing traffic, the lesson will get across and the kids may get a workout. But they won't be moved to dance--or to think. For example, they are never asked to consider why legs come in pairs.