My dog is polydactyly; she has extra toes.
Wow, I've never heard of that before!  How many extra toes does she have?
Three.  It's unusual with dogs, though.  Cats along the East Coast of North America are often polydactyl.
Interesting!  Are there other animals with this phenomenon?
Yep.  It's a congenital physical anomaly that can also happen in humans!