This isn't just the least-fun thought experiment, it's a medical malady common enough to have its own name. Learn how internal hirudiniasis works (and why you don't need to panic if if happens to you) in this episode of BrainStuff, based on this article: https://animals.howstuffworks.com/marine-life/swallow-leech.htm

How Can Rhubarb Grow in the Dark?
10:28

How Does the Blue-Footed Booby Work?
08:41

Who Was Helen of Troy?
07:27