Once there was this concert performed by a piano accompanist and a French horn player. And the accompanist had a page turner. As you may know, the page turner sits on the left of the accompanist. Every time when the page turner had to turn pages, he was always turning from the bottom of the page which right covered the music at the bottom that the accompanist had to see. After a while, the accompanist got annoyed, so he whispered to the page turner, "from the top, from the top... ps... from the top"... so the next time, the page turner turned all the way back to the beginning...

I will assume that this joke will be easily understood by musicians......