Derived from Pecorino, its fermentation is brought up to quite a decomposition by the development of the larva of the Piophila casei, a small insect. Its pasta becomes very soft and some liquid comes out ("lagrima" = tear).
Due to the high content of living organisms (really little jumping white worms), it obviously is not a product generally suitable to anyone (it might cause allergies) and in some countries it might be illegal to produce or sell it.
In Sardinia this is intended instead as a precious good, illegally sold (more or less) at three times pecorino's price.
See also: List of cheeses