Casu is cheese in Sardinian, and two kinds are listed in the Slow Food Presidium.
Casu Axedu, made all over Sardinia, is a soft uncooked cheese shaped into rectangles and generally eaten the next day. It can also be preserved and steeped in brine, when it becomes Fiscidu (or Fruhe, Frughe, Frua, Merca, Viscidu, Ischidu, Bìschidu, Vischidàle, Préta, Piéta, Casàdu, Cagiadda, Casu Agéru, Casu e fitta, Latte cazàdu or Latti callàu). It's designated PAT.
The notorious Casu Marzu 'rotten cheese' (pictured in the icon above) is another uncooked sheep cheese left to go off and infested with maggots of the Piophila casei (cheese fly). As they eat the cheese it becomes very tangy and creamy. The larvae measure .3 inches and by the time a cheese is ready, there are thousands swarming inside. When disturbed they jump up to 6 inches; even so, some diners prefer to eat it with the maggots in it. If the maggots have died, the cheese is no longer good.
It is usually spread on traditional carta da musica, and believed to be something of an aphrodisiac.
Images by formaggio.it, Shardan