Imagine that you have a deadly infection, and your doctor gives you medicine made from lizard spit. Or a dog attack destroys your face, so doctors peel it off and stitch on a transplant. Or you wake up from surgery only to find leeches feasting on you. Or to battle your cancer, doctors insert tiny tools that race through your blood stream to zap the tumor. Where are you? Ancient Egypt? Frankenstein's lab? Another planet? No, you're on Earth in the...