I was petting Finn today and when he rolled over I noticed a strange patch on the pad of one of his back feet. It doesn't look like anything on any of the other pads and I don't know if it's a problem or just a callus and I'm overreacting. I took the best pictures I could considering the bad lighting and a dog that won't sit still. It's a white spot with black specks on it. It's on the right at the edge of the pad. Does anyone know what this could be?