I've just found this thread, i've read it from start to finish and now my brain hurts!
Try this one:

if a pianist turns their back to the keyboard,(with their hands behind them)it's difficult to play because the keyboard is back to front, OK! if the pianist crosses their arms whilst having their back to the piano, it makes playing a little easier. If the pianist is upside down with their back to the piano keyboard they should (if they rotate their wrists thru 180)be able to play as normal.
Anybody care to try it???

T