Can I steal my parents cat and get away with it?
Do you think your parents will notice?
No, and I think they'll love my new pet.
I see two things wrong here.  First, you stole a pet, and second you betrayed your parents' trust.  Both of these things are wrong and you should apologize and return the pet immediately!
I'm keeping that cat.
You can't truly believe that your parents won't notice you have their cat. Even the cat knows who its real owners are!