The formula is one you've seen before (if not, say good-bye to your loved ones now), the basic idea is to align three of the same type of animal by moving one into an adjacent square, either directly up and down or left and right of its position. The basic story is they all need to be in their pens and each square needs to have an animal hustled off of it. This means that along with making combos and so on, you also need to use each square on the grid at least once.