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!  
Really?  Awesome!  Are there certain breeds of dogs that have this, or can it happen with any breed?
Well, my dog is a mongrel, so maybe just mixed breeds?
Is it wise to remove the extra toes, or is it better just to leave them alone?
Polydactyly
Polydactyly or polydactylism (), also known as hyperdactyly, is a congenital physical anomaly in humans and animals resulting in supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly (fewer fingers or toes).
Signs and symptoms.
In humans/animals this condition can present itself on one or both hands. The extra digit is usually a small piece of soft tissue that can be removed. Occasionally it contains bone without joints; rarely it may be a complete functioning digit. The extra digit is most
Polydactyl cat
A polydactyl cat is a cat with a congenital physical anomaly called polydactyly (or polydactylism, also known as hyperdactyly), which causes the cat to be born with more than the usual number of toes on one or more of its paws. Cats with this genetically inherited trait are most commonly found along the East Coast of North America (in the United States and Canada) and in South West England and Wales.
Occurrence.
Polydactyly is a congenital abnormality that can be inherited as an autosomal dominant fashion