scarily enough, that can happen. occasionally, a person has more than one embryo when they become pregnant, but the extra embryo is unable to survive or is absorbed by the other embryo. sometimes it's not absorbed completely, and things like this happen. i find it surprising that they found out about it seven years later, though. i guess it's a less visible form of siamese twins. still creeps me out. if that type of thing can go on for seven years without anyone knowing, it might even be able to go even longer. in some cases, absorbed embryos can cause the person to have two sets of DNA [their DNA, and their sibling's DNA, i guess], which i think is really neat.