Well, it depends on what you mean by "serious medical procedure." Administration of a placebo is a serious medical procedure, too (it is the surgeon who is a quack, if surgery is unwarranted), as when a doctor used to give an insomniac a prescription for pills that unbeknownst to them contained only sugar: they worked. When the shaman extracts his object--the frog, stone, or whatever--by trickery, and the patient believes and gets better, that's pretty much the same. Metaphors cure, especially with patients who don't understand that they are metaphors. In medieval and Renaissance Europe, I imagine there was just enough of an incision, done with enough medical-sounding talk, to make the patient believe that his skull had been opened, and then, voila, it was just like pulling a tooth. Sometimes, it's the care and concern that heals, along with a change in one's outlook (these days, it's called "cognitive-emotive therapy"). Tarot readings sometimes work that way, too, I think.