Nothing, some dogs say it is because the blood source is close to the ancestors, but it is actually an atavism. Especially many sled dogs have six fingers.

For them, it is normal that atavism often happens. If it will affect the normal walking and running, minor surgery is needed, if it will not affect it, it is completely unnecessary. First of all, don't be superstitious. People also have six fingers, which are deformed and can be plastic surgery. In the countryside, some dogs have white tails, and their owners will cut off their tails, because if they don't take good care of them, they will die.