Rats
If you see rats, they seem to be playing at all times. They are very social animals. They seem to not run out of energy. They love playing tug of war with other rats. They even wrestle with each other at times. The reason why they are happy creatures is that they have very strong bond with their family. Their mothers spend a good deal of time attending to their needs the moment they are born. The attention and care that they get from their moms play a huge role why they are happy creatures.
