I don't know what the deal is, but my fingernails barely grew at all last week. As I recently mentioned (twice, actually; you'd think I had a creepy finger fetish), I clip my nails reliably on Fridays. But right now my fingernails are about the same length as if I had just clipped them. They don't seem to have grown at all.
I find this very weird. Perhaps it happens more often than I realize, and I just have never noticed this until now.