I’m sure most of us have heard that while filming the scene where Hans gets thrown from the roof in Die Hard, Alan Rickman was expecting a 3 second countdown and they dropped him on 2 to get a genuine surprise.
I’ve also heard that the “funny like a clown” dialogue of Goodfellas was left out of the script and rehearsals so that everyone’s had a genuine awkward response to the interaction between Ray Liotta and Joe Pesci.
On the darker side, Stanley Kubrick basically terrorized poor Shelly Duvall on the set of The Shining. Definitely immoral, but she also gave a fantastic performance for that movie (not justification for her treatment, just an observation).
What are some other examples of this?