I don't have a pet, but if I did then - what with Sarah's allergies - it would in all likelihood be a goldfish.
A goldfish with thumbs would, I suspect, be of great interest to biologists everywhere who would regard it as some kind of missing link. I'd probably make a mint. So, there y'go - if my pet had thumbs, it'd make me lots of money. Yay me! And indeed yay goldfish!