Earn thirty stars from the three available on each level to unlock the second and third environments. There's an Undo button for rewinding turns, but you can only score one star if you use it - so it's only handy for getting familiar with the layout of longer levels. Tapping on Yello if he's trapped under fallen debris will free him before you take your next shot. Using the pinch controls to zoom in and out of levels is the best way to work out the most effective route back to the bowl.