Nicholas Cage in Birdy
This is one of the most extreme things an actor ever did in preparation for movie roles. For his role as a suffering veteran in the acclaimed movie Birdy, Nicholas Cage inflicted physical pain on himself, to sympathize with the pain of this character.
He did what many of us would consider a proper nightmare – having a few teeth pulled out (without anesthesia!), and as if that wasn’t enough, he walked around for several weeks with his head wrapped in bandages, causing his skin severe infections.