If only you could use it all alone, right? To know for sure if something freaky was up? If two or more people are using it, one of them ALWAYS screws things up and moves it. Every time I tried to mess with one, I could tell who was pushing it by their facial expressions.

Of course, there's always the chance if you did it by yourself, your subconscious would make you spell out something weird anyway, and you wouldn't even be aware....