Fascinating!
To go back to a previous question, does anyone actually abide by this regulation? I've been frequently flying in US airspace for a decade or two and have never heard *anyone* wearing an oxygen mask (you can tell, you know!). Especially as the vast majority of jet traffic is FL350 or above... There must be many a time where one of the pilots has nipped back to the loo and the other needs to make a radio call?