Aniello Arena, star of the film Reality, which is premiering at Cannes, filmed his role on some sort of special leave from the Italian prison where he's serving a life sentence for murder (actually double murder, which is twice as bad as regular murder!!!).
Apparently director Matteo Garrone discovered Arena in a performance with his prison theater troupe, the Fortezza Theater Company, which has a dispensation to perform in theaters around Italy. Reportedly, Arena (who plays a small-town fishmonger whose life is upended by reality TV) is very good:
Peter Bradshaw, critic for the Guardian, singled out Arena's performance in his review: "[T]here is a very winning central performance from newcomer Aniello Arena as Luciano, who has a sharp, calculating and very mobile, open face, which registers every jolt of fear, of hope, of triumph and dismay: the face of a would-be comedian who can do everything but make people laugh."
Unfortunately, Arena could not make it to the Cannes premiere, because he had to go back to being in Italian jail for the rest of his life.