Play the mission when you go to the hospital to protect the Don. After you 
kill the first assassin
and Michael Corleone tells you to go to the basement, go foward and make a 
left. You should
see a door with Michael Corleone talking to Vito Corleone while he is in the 
hospital bed.
Listen to the conversation carefully. This is the real Marlon Brando 
talking, recorded while
he was hospitalized.