strangewood:

Do you improvise a lot while filming?
Nicholas Ray: The entire ending of In a Lonely Place, for example, was improvised. In Rebel Without a Cause I improvised, one evening at home, the whole scene where Jimmy returns home to his parents after the tragedy. The scene had been bothering me a lot: according to the script it should have taken place in the mother’s bedroom, but it seemed so static to me. So one evening when Jimmy dropped by to see me, I began to discuss the scene with him; I asked him to go into the yard while I played the part of the father in the living-room. I gave Jimmy two contradictory instructions: first to go upstairs without being heard, and then, at the same time, to feel the irresistible need to talk to somebody. I then turned on the television to a channel where the programmes had finished, and pretended to be asleep. So Jimmy comes in and walks past me to go upstairs and it’s then that the contradictory movement gets the better of him: he falls heavily on to the sofa, with a bottle of milk, and waits for me to wake up; at that very moment I exclaimed, ‘Now your mother comes down the stairs!’ And I knew that I’d found the dynamics of my scene. I got the designer to come to my place, and the set we used in Rebel was copied from my own living room where we had improvised the scene. It’s a very satisfying way to work; it was also from this that we got the idea of showing the mother coming downstairs from Jimmy’s point of view. The planetarium, the kids in the car, and several other scenes were also improvised.

[Interview with Nicholas Ray, Cahiers du Cinéma 89, Nov. 1958.]