TOD: The two experiences that come to mind in terms of stage experiences that make you just hold your breath and try to get through the scene (other than already noted experience) come from when I was back in Prescott.
1) I did a production of
Fiorello! during my sophomore year of high school at the PFAA (the community theatre where my mom just did
Suburb). For those of you who are familiar with the show, I played Neil, the young up-and-coming intern for Fiorello, but I also doubled as a "Hack" in the poker scenes...which put me in about every scene. To distinguish the characters, I had on a big fake moustache for when I was a "hack" (I see the jokes coming from this a mile away, der Brucer

), and on our opening night, during "The Bum Won," of course it decided to start slowly and comically sliding off my face. Luckily I had a newspaper which I promptly threw up in front of my face, as I was laughing away as well as a couple of the other guys in the song. The audience, of course, ate it up, as they watched me inch my way back behind all of the other guys, but the best moment came near the end of the song where as we were exiting, the moustache very obviously fell out from behind the paper and I had to step on it and slide it off.
Then shortly thereafter in the last scene, "Morris" starts off the scene where he's on the phone with his wife...only that night, our "Morris" misjudged the time he had and when the lights came up, he wasn't on stage (later we were told he was in the bathroom) and so all of that were on stage did a quick check-in and wondered how we were going to cover. So I quickly ran up to the phone and started improvising some of the dialogue that I happened to remember of the conversation that he has with "his wife" and did so until I saw him ready to make his entrance, which he did and threw the line to him "Morris, your wife's on the phone and she's really going on about you not being home and with the kids..." and he took it and started his lines and we made it through safe and sound. Later that evening he wrote on a one-dollar bill "Thanks for saving my ass" and gave it to me - as my first professional dollar I ever earned working in the theater.

2) During the run of "Fiddler" I did as a senior in high school, the big "Tevye's Dream" sequence, as any of you who have done or even seen the show, can be a nightmare (pun intended) to stage. Our technical designers went back and forth on how to have Fruma Sarah come in - should we fly her? Should she come up from the stage floor? Should she be on top of something? It was finally decided that she would be sitting at the top of a ladder, strapped in, while the ladder was secured to a dolly navigated by someone underneath the ladder, and all covered in black material. We worked it over and over to make sure the girl underneath knew what was going on and it was all safe and comfortable for all concerned.
So, we get to the 4th show in our run, and sadly no one had the foresight when we had teched the number to remember that there was going to be dry ice machines pumping out fog on either side of the stage, one strategically placed right near where Fruma Sarah makes her entrance. For those of you that may not know, dry ice machines (as opposed to fog machines) create condensation right around where they blast out the fog...
About 5 seconds after Fruma Sarah comes out, we all see the whole thing start to topple over and panic ran through everyone of our hearts. Thankfully they were far enough away from the pit that Fruma Sarah didn't fall into that, and in fact she just kept on singing away on the ground. The girl underneath was really shaken up, but not hurt - but it brought the show to a halt. They closed the curtains, and the tech people ran out to check the two girls. Once we had everything under control, our director went out and made an announcement to the effect of "Live theatre, what can you do, right?" Then we took the scene from the top and Fruma Sarah came out sans ladder that time - and did so for the rest of the run.
Needless to say, when I (playing Tevye) am trying to figure out with Hodel and Perchik how to break the new to Golde that I've given them my blessing later in the show, the line "How will I tell your mother? ...Another dream?!" had a WHOLE new context, and managed to get a huge laugh out of the crowd.
