Well, there is no serial number.
Its legal to look online! So, stop. You can get in trouble.
Usually, you don't need catz 4 serial number..
But, there's this one....
06750894hgvnf8547
:) Enjoy. (Serial number made by: Petz Dogz4Catz serial number maker)
I made this program by myself, make serial numbers your self, and they work!!