An extra-toes cat isn't a breed but any cat born with polydactyly, a harmless genetic variation that adds toes to one or more paws. A typical cat has 18 toes, while polydactyls often have six or seven on a front paw, sometimes forming a mitten-like thumb. The trait is dominant, so one affected parent can pass it to roughly half a litter. It's especially common in New England and Atlantic Canada, where ship cats with big paws were prized as mousers.
The nickname comes from Ernest Hemingway, who was given a six-toed cat named Snow White; dozens of descendants still live at his Key West home. Most extra-toed cats waiting for homes are domestic shorthairs or longhairs, with moderate shedding and personalities as varied as any cat's. The main care difference is claw trimming, since extra claws can curl into the paw pads.