Did you happen to listen to Radiolab this weekend? There was a fascinating story about a woman who had merged with her twin's embryo inside the womb. This caused a siamese twin living inside one body. The woman's internal organs were half her own, and half her twins, with two different sets of DNA .... and two souls (ok ok, maybe not the soul part). Perplexing, a bit spooky, and stuck inside my brain.