What do emoticons above animals mean?

You will find a new animal that needs help at every location you visit. When you meet the pet for the first time you can see a sad emoji above it. As you progress through the levels, you'll be able to help the animal. It's mood will get better and a smiling emoji will appear above it and you will receive a reward for this.
After you helped the animal, tap a smiling emoji above it and you'll get a reward. Some animals give you an "infinite lifes" booster, other animals will give other useful rewards.
This "infinite lifes" booster will be valid for 30 minutes from the moment you receive it.