I just heard a story about a woman returning milk to a store insisting that--despite the fact that the expiration date on said milk was nowhere near happening, and despite the fact that the milk smelled fine, and despite the yet more bewildering fact that one of the two bottles she was returning was not even open--the milk was bad. Her reason: her son, who apparently has never been sick in his life, drank the milk, then vomited awhile later. In this vomit, there seemed to be chunks of curdled milk. Yes, the milk had curdled in the stomach of this boy (who may or may not also lay golden eggs). In the head of this woman--who I'm sure is a lovely person--this meant the milk was somehow bad.
Nay, fine woman! Instead, you have bore witness to a magical feat indeed, for this lad had made cheese right in his stomach!
Well, as you may have guessed, the milk was not bad, or at least if it was this is not what made it curdle. For inside the brave young boy's stomach was a complex of enzymes and acids, not unlike the rennet (harvested from the stomach linings of young animals, as well as some vegetarian-friendly sources) that cheesemakers use to separate milk into curds and whey. That milk, good or not, inside a warm stummy with all kinds of digestive acids floating around gets broken down into parts that look a lot like this curds and whey situation in the cheesemaker's pot, making the milk digestable and the nutrients absorbable, and this lady simply was lucky enough to see it up close. Could have been a good teaching moment. But hey, she got her seven bucks back, and junior got out of school. Of course, if that milk is curdled before drinking, that's a different story...but here's trusting our senses to protect us from that one.