My aunt had a cat with opposable thumbs.

It made for a great conversation starter, because you would throw it a sardine and instead of bowing down to eat it. The cat would pick it up, and bring the fish to its mouth.

However, when I first read this topic's title, all I could think of is how my two cats both love to eat toes and nipples. If either are exposed, they will "bite" them. Its quite funny, because you will see them look at it and ponder it... then chomp.