The Huge Plot Hole That Isn't, Really (SPOILERS)

How the hell does everyone come down simultaneously with the isopod infection, and on July 4, to boot? If larvae had been in the drinking water, you would have seen a gradual ramping up of cases over an extended period of time, not 700 infections the first day of the epidemic.

As it so happens, this is trivial to explain, so trivial that I suspect the explanation was in the script and maybe was even shot, but then omitted from the final cut.

It's pretty clear that someone at the de-salination plant screwed up the water filtration so that it failed at about midnight the night before the 4th, allowing the larvae into the town water supply. It takes 8 hours for the larvae to grow into adults, so the first victims become symptomatic at noon, having been early birds who drank tap water at 4 AM. And that there would be a screwup right before the holiday is credible, because maybe the worker was distracted by holiday plans.

I'm guessing that they decided that they could cut all of this out of the movie because, after all, none of it is scary in itself ... but it would have made the film more credible and hence scarier for people (like me) who notice scientific plot holes. I figured out the above while driving home from the theater ... but while I was watching it, it didn't ring true as a real epidemic to me.

Prepare your minds for a new scale of physical, scientific values, gentlemen.