A very rare occurrence
It turns out that the color of the dog’s fur was not due to some bizarre illness or extremely rare and dangerous virus. It was actually just because of something called Biliverdin, which is something that all dogs have. But for some reason, Rio was a special case and not just any average dog.
Biliverdin is the green-colored bile that can be found inside a female dog’s womb. No one can say for sure just what exactly it does and its specific purpose, but it is a real thing and completely normal. The news came as a huge relief for Louise and Claire, but that mystery of the green fur still needed a further explanation.