Same question! There's a sort of thud when you step on one of the buttons, as though something is trying to move but can't. Maybe you have to use a stinker to press both buttons at the same time while some of the bridge tiles are down.
Again I'll say...it's not fun if you can't
see the puzzle.
![Wink :wink:](./images/smilies/icon_wink.gif)