Yeah, I'm not so sure this would be a case of siamese twins, but rather a mutation probably due to conditions while in the egg. More than likely lacking an inhibitor which would tell the cells to stop dividing...not sure, ill have to give my brother a call and ask him on this, he's had a couple of 2 headed turtles, both from batches that were screwed up during the incubation process due to power outages when we had hurricanes here in florida...wonder if its something like a flat worm, but only happens in the early stages of the developing fetus. (Flat worms multiply easily from being split in half, and if you just split the head, it grows two)so if that were the case, maybe during the cell division process, something went wrong and rather than staying together, the two cells that originated from the one, went off and made their own heads due to some physical/environmental barrier? Like I said, ill ask my bro. Lol, he's a herpetologist.