1. Ren & Stimpy
What we thought they were: An anorexic mouse and a red Tasmanian devil
Why their species was ever in question: Mainly because they're both extremely bizarre-looking individuals. On first inspection, Ren (left) appears to be either a rodent or a worryingly emaciated Siamese cat, while Stimpy (right) could be mistaken for a badger or some sort of wild dog, but is also the exact same shape as Looney Tunes' Tasmanian devil. Amusing, yes. Confusing, also yes.