Why Remus Lupin Isn't A Rabbit

Everyone in the school has heard of the Gryffindor boys' "furry little problem", courtesy of James Potter and Sirius Black. According to most rumours, it's a naughty rabbit. But no one thinks to ask the obvious question. Since when does Dumbledore allow rabbits as pets and why hasn't anyone ever seen it? That is because there is no rabbit. This is why Remus Lupin isn't a rabbit.