Dinner-plate size blood stain? You'd think the police would be investigating a murder by now... If the couple's story holds up, it'd go way beyond cleanliness and Perry Mason would be called in? I mean, that's some big bloodstain, not like someone having a paper cut, eh? And as rthib pointed out, this blood ain't your quick dry variety either.
Kind of reminds me of the lady and the hot coffee at McDonald's, if you ask me....