This wonderful story is a great example of how the entire world is a single unit.
Ganesha was known to be a mischievous child and he would indulge in a number of naughty activities. One time, he came across a cat while he was playing, and proceeded to mess around with it. He picked up the cat and threw it on the ground, pulling its tail and having fun with it, while the cat meowed in pain. Ganesha failed to notice it and played around until he was tired and then came back home.
On reaching Mount Kailash, Ganesha was shocked to see Parvati lying down outside the home, with wounds all over her body, and crying in pain. Ganesha rushed to her and asked her who did this. To which Parvati replied that Ganesha himself had done this to her. The cat was actually a form of Parvati, and she wanted to play around with her son. But Ganesha treated her unfairly and ruthlessly and his actions on the cat have reflected on his own mother.
Ganesha was utterly sorry for his behaviour and took an oath to treat all animals in a gentle manner with care and affection.
This story gives a very important lesson that does unto others as you would want others to do unto you. And this also includes animals, being careful of them, and not causing anyone any harm.