Actually, I think that sort of thing actually happens pretty often, even if mostly what you get is something like a cyst with teeth in it (I think there's an Atwood short story, Hairball, that makes use of this phenomenon.
Far spookier, to my mind, are lithopedions - Stone babies (http://www.answers.com/topic/stone-baby).
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Check out the following link for the details.
http://news.bbc.co.uk/2/hi/south_asia/4624307.stm
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Far spookier, to my mind, are lithopedions - Stone babies (http://www.answers.com/topic/stone-baby).