Pacino's silent scream is just heartbreaking along with the follow up scene of him sitting as an old man thinking back about all the woman that he loved and lost because of the life that he chose.

Another moving scene is when Vito rises from his sickbed and finds out from Tom that Sonny has been killed. Brando is just superb in that scene. Watching his facial expressions magically transform from a concerned man, to a heartbroken man, and back to the man in charge, in a matter of seconds, is just amazing.

Pacino's expression of pain from the silent scream and Brando's silent expression of pain from hearing the news of his son's death are probably the two best displays of emotional pain in the entire trilogy.