According to 7-time Academy Award winner and Hollywood Legend, Robert Duvall. The Godfather himself needed his lines very close to where he can read them off.

Some people write their cheat sheets in their hands. The Godfather, Marlon Brando apparently wrote them in a Tree??

Pretty interesting stuff from Mr. Duvall as he walks to get some lunch in Beverly Hills.

Check out the rest of the clip when he was asked about a Godfather remake.