I saw Don Giovanni live at the opera yesterday. At one point, one of the background people ran through the scenery, and a couple of minutes later he was about to do the same when he was apparently caught by a colleague and told that everyone could see him (at least he didn't show up again). I found it highly amusing, but it didn't make me lose track of the actual opera.
Oh, I hate it when that happens. Being backstage myself, I am incredibly paranoid about what is or is not visible that should not be. People look at me strangely when I ask them after the performance if they noticed anything like a blank spot in the scenery or a stagehand walking through the scenery.
And you saw Don Giovanni? What was the main cast, would it be too much trouble for you to list them?