The best place to look for them in film is around the end of the "second act" where a characters world is turned figuratively or literally upside down.
The first one that popped in my head was the famous "my daughter... my sister" scene from Chinatown. Jake, our hero, reacts with violence at what his brain just cannot comprehend. Evelyn asks if he can understand..."or that just too much for you." It is.
The second scene that came to mind was a scene from another Kubrick film: The Shining. Nope. Not the "Here's Johnny" scene. But the scene just before it. Shelley Duvall comes into the room where her husband Jack has been spending months isolated from the world "working on his novel." When she trespasses into his work space she leaves behind any hopes she might have held, or delusions she might still be clinging on to. She reads the words of her husband's book and her life is destroyed forever.
These moments don't have to be filled with terror though. There's a great moment of transition for Scout and Jem in To Kill a Mockingbird.
For the first half of the film they are convinced that Atticus, their father, is about the most boring man in town. Then the day comes when a rabid dog comes into the neighbourhood and the Sheriff calls for Atticus to come from his law offices to shoot it. Atticus aims, takes off his glasses and throws them to the ground and brings the sick animal down in one shot.
His children are amazed. They didn't realize their soft spoken father was "the best shot in the county." Their world isn't what they thought it was.
It's a great scene that foreshadows the climax of the film, when Boo Radley comes to save Scout and Jem from a mad dog of an entirely different sort.
What about you... Any great character transition from films that haunt you?
