I was in a play in high school (the only one I've ever been in) and I got to play the youngest child. I also had the last line of the play, which was:
"Maintenant, c'est VRAIMENT vous qui l'avez tué!"
which means:
"Now you've REALLY killed him!" after a fake gun was fired backstage.
I was REALLY good at memorizing the lines.
Once, during a showing one afternoon, a bee flew onto the stage. I'm scared of them, like, I have a PHOBIA of them. The buzzing freaks me out. So it lands on the stage, right beside where I have to be sitting, and I choke on my line.
Another actor in the play improvises for me, saying, "Oh my goodness, it's a BEE" and gives me a look, like, "LINE!" But, not being a great improvisor, I grab the closest object (a book) and SLAM it down on the insect. Needless to say, it was a bit of comic relief for the audience...