Maybe it's just me, but I still don't see what sound had to be on for, unless you are somehow testing to see if the user has the tab muted. (I'm using the in-browser version, which I assume is obvious in view of my speaking of muted tabs.) I could have had the volume turned all the way down during that time and I can't figure any way it would have made any difference.
I can understand that flavour of tunnel vision. I have it myself for my own software: what seems obvious to me often isn't to others.
Thanks again for a very enjoyable game!