"In 2015, a young woman began to have headaches. They discovered that she had a brain tumor, and when the doctors removed it, they were shocked to see that it was a lump resembling skin that contained bone, teeth, and hair. But this was no parasitic twin: the mass was called a “teratoma,” or “monstrous tumor.” When the woman was an embryo, some cell tissue fell off and ended up where wasn’t supposed to be, her brain. It then develop hair and teeth while the rest of her grew as normal."