In a normal game, you are advanced to the next level once you remove the required number of animals from the board. On the first level, three of each animal is required; on the second level, four are required, and so on. A rabbit is thrown into the mix on level seven, making things even tougher. (Rabbits may reproduce like mad, but never where you want them to, here.) If one type of animal is left out, or the last to be removed, you may notice a distinct change in temperament.