It's just that. Are you the product (offspring) of a coupling of your mother and brother, Father and sister or any combination thereto?
To my knowledge, I've only met one person who was the product of such a union. He was a teenage boy who attended the Boys' and Girls' Club. It was common knowledge and I even asked him about it in my own sheepish way. He confirmed that his mother and her brother were fooling around and she got preggers. He had 11 toes, 5 on his right, 6 on his left and distorted pupils.
Anyway, I'm not asking because I want to embarrass you or anything. I'm just curious. In fact, you don't even need to reply to the thread but if you could PM me and tell me about your experience.
And Tim, we already know. You're not a product of incest.