anchor.diff:      coords.add(newHead);
   
       assert(coords.length >= oldLength);
  -
  -    newHead.paintBlack();
     }
   
     void render(canvas) {
  
positive.code:     if (coords.length == maxSize) {
        print("Maintaining  tail");
        coords.removeAt(0);
        /// Nuke tail.
        tailCoord.paintWhite();
      } else {
        print("Growing tail");
      }
  
negative.code: 
    gameLoop.start();
  }
  