⋮
       ⋮
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Four legs
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Two legs
       ⋮
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Two legs
Palanquin
       ⋮
Two legs
Palanquin
wheels  
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Two legs
Palanquin
wheels  
Horse cart
Boat
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Two legs
Automobile
   Train
    Plane
    Ship
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Two legs
Automobile
   Train
    Plane
    Ship
Spaceship
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  Two legs    
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   ?!?!
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