- Start with an animal you dislike. Maybe it's ugly, or seems to have no purpose, or it's only ever been a nuisance to you. Whatever animal (or insect) that is, hold that image in your head.
- Pick out one or two physical characteristics of that unliked animal and give them to your otherwise human character. Your protagonist, then, is part-human, part ugly-pointless-hated-nuisance animal.
- Place this protagonist in a world in which his or her mutations are unique and rare but not uncommon enough to be noteworthy. These types of mutations are as rare as, say, Crohn's Disease or Type 1 Diabetes.
- Send your protagonist on a job interview.
What type of job would your protagonist apply for? Would he look for a place where the special abilities granted him by his mutations could be put to good use? Or would he try to fit in by playing up his human side and downplaying his differences?
How do other people react to your protagonist? How is she treated differently, both legally and individually? At what does that do to her self-image and self-esteem?
A story like this could be written in a number of styles, all of them valid and interesting. You could place your protagonist in a DC- or Marvel-esque world of superheroes. Or it could bend into absurdism (think Kafka), or feel more surreal (thinkWilliam Burroughs), or land squarely in magical realism (think Isabelle Allende). Pick a style and run with it.
Ulterior motiveI've long believed that the purpose of literature is to teach us how to be better human beings. I've also noticed that the stories that teach us (or at least me) best involve characters and situations that are unhuman or inhumane. Asimov's stories about robots and artificial intelligence are a perfect example. So are first contact stories, dystopian fiction, and even superhero comic books. (Sorry, graphic novels.) What they all have in common -- the good ones, anyway -- are the interplay of the flaws and strengths of being human. They get at the heart of what it means to be human.
This prompt is just one way for you to explore this concept of what it means to be human. What can you teach yourself?