My wife is a veterinarian, and loves the show, but is kind of cheesed off on that one.
Well, that blows the plot hole open wider. Modern veterinarians are all trained in food safety (as vets are hired to do inspections of meat production). There is no way in heck that a vet wold allow anyone to eat of an animal that died from unknown causes in that situation. That's just *stupid*. So, either they're hauling a full-grown dead pig around behind Hershel's back for butchering, or the writers are dumb.
Symptom onset for flu is typically quick - 12 hours would not be at all incongruous.
In children, gastrointestinal symptoms are common with flu. With the lighting as it was, it was not clear to me that he was vomiting blood.
The flu doesn't even need to kill him directly (if the writers actually refer to any real medicine). He was clearly running an extremely high fever, which is bad enough. The water in that shower was unheated. Dumping cold water on an overheated person is *BAD*. All we require is that he faint, and whack his head on that concrete floor. A head injury enough to kill a human may not be enough to stop him from reanimating, and rampaging....
Oh, and anyone else note how he was coughing and snotting into the water barrel?? Contaminated water is funfunfun for the whole family!
