Which actors in the film did not follow the script, but achieved unexpected plots?

For example, in "White-hot" (1949), the gangster Cody (played by james cagney james cagney) made a scene in the prison dining room, and all the cast members were frightened by cagney's performance. That's because the script for this scene was not written well, and cagney had to improvise. He asked the director to arrange two burly extras to sit next to him (later, he jumped on the table with their shoulders) and told the photographer not to stop shooting no matter what happened. In fact, director Raoul Walsh doesn't know what cagney is going to do, let alone other actors. When cagney's little universe broke out, everyone was shocked ... The play became one of cagney's most memorable performances.