I read the first few chapters of Garry Wills' Why Priests? last night. I chuckled a bit when I read about a "heresy" I didn't realize I was guilty of (to add the many others I'm very much aware of), namely that of the Stercoranists. These dangerous heretics asserted that the bread and wine of the Eucharist, after being ingested, were subsequently digested and then excreted. You know, like food.
So, if they're not digested (and excreted), then exactly what does happen to them?
Well, that's one of those questions you're just not supposed to ask, apparently.
It's best not to think about it.