Not all snakes have the same kind of scales along their backs.  Some 
snakes have scales which feel smooth to the touch while others have 
scales with a ridge along the scale (keeled).  The difference between 
smooth and keeled scales is quite obvious.   


  
A. Snakes with keeled scales 
             
             Keeled scales


B. Snakes with unkeeled scales
             
             Unkeeled scales