Six Toes
Some breeds of dogs, such as the Norwegian Lundehund, have six toes on each foot, which can make them more agile and able to grip objects more securely. This is due to a genetic mutation called polydactyly, which is responsible for the extra toes.
These extra toes are thought to be an adaptation to the rugged terrain and steep cliffs where the breed originated, as they provide extra grip and stability when climbing.