My initial idea came from the 'medieval beasteries' which were illustrated manuscripts that were based on parables about animals. There was one called 'the book of beasts' which I like the sound of. The parables were based on the behaviour of the animal, but because they had only ever heard some of these animals described they got creative with their descriptions of them. For example they thought there were such things as unicorns, dragons and sea monsters called 'sawfish'. They're full of random stuff like this: "The wolf may not bend his neck backward in no month of the year but in May alone, when it thundereth." You have to love it.
My ideas branched off a little and my illustrations became portraits of people dressing up as these animals, seeing as the animals themselves were metaphors for human behaviour. There's lots more I want to do with this whole thing but it might take a different form or style when I approach it again. I'm not quite done with it yet... yes, that means more human/animal stuff, I apologise in advance : )