Marlon Brando could have only achieved his heightened performance in On the Waterfront with the help of his film coaches, such as Talking Terry, shown in this historic footage.
(this is the Talking Larry iPhone app, a fun little diversion of mimicry; and it can record performances as video, even upload to YouTube).
If you re curious if this worked out well, see the performance
http://www.youtube.com/watch?v=l0waNRaz6wU
