What the hell is it?
This, dear reader, is a medium-sized lump of Sweet Fucking Christ. Casu Marzu is a sheep' milk cheese that has been deliberately infested by a Piophila casei, the "cheese fly." The result is a maggot-ridden, weeping stink bomb in an advanced state of decomposition.
Its translucent larvae are able to jump about 6 inches into the air, making this the only cheese that requires eye protection while eating. The taste is strong enough to burn the tongue, and the larvae themselves pass through the stomach undigested, sometimes surviving long enough to breed in the intestine, where they attempt to bore through the walls, causing vomiting and bloody diarrhea.
Wait, it gets worse ...
This cheese is a delicacy in Sardinia, where it is illegal. That' right. It is illegal in the only place where people actually want to eat it. If this does not communicate a very clear message, perhaps the larvae will, as they leap desperately toward your face in an effort to escape the putrescent horror of the only home they have ever known. Even the cheese itself is ashamed; when prodded, it weeps an odorous liquid called lagrima, Sardinian for "tears."
Danger of this turning up in America:
There is significant danger here, as we're thinking the cheese companies have a lot of maggot stock in the back of their warehouse they'd like to get rid of. And, there may actually be a market for it. Self-loathing is a powerful force in this economy (see the diet section of your local supermarket) and there' times you get low enough that, damn it, you feel like you deserve nothing better than infested cheese.