I looked on Yahoo Answers and read real life experiences from people. I picked one on a funny theater rehearsal. A high school was working on their school's musical. The main character of the musical was center stage, starting his solo, when the stage collapsed from under him. After all that, the guy stayed in character and kept singing his song, he though he was no longer on stage, but IN the stage.
Another story was how a man forgot his lines during a play, and decided to make up his own lines. The other people on stage were confused because what he said didn't make since at all, but the audience couldn't tell the difference.