In 2006 two of our cats, Valyn and Pixel, died from liver failure six months apart from each other. We hoped upon hope that just those two had gotten into something or that it was just coincidence that they both died of the same thing; thankfully at the time none of the others were showing any symptoms.
I've never seen our 4yo so eager to tidy up than today when he, on his own, started tidying up because his cousin was coming to visit. We'll keep that one in mind for the future!