When you have collected all the animals you can get free boosters. The green level in every episode is where you need to have 3 stars for the animals; Thanks Brenda Bear :)
Hey candycrushking! I had a tough time with that level too :) Here´s a video that I found which helped me a lot to pass the level. Good luck https://www.youtube.com/watch?v=W13ha1CCSg0