About 10 years ago on local TV an airliner of some sort returned to the local airport with a rubber jungle deployed after a problem with the ECS system of some sort. They interviewed some of the pax deplaning and one of the aviation experts stated: "Well, the oxygen masks came down, but I don't think they were working because my ears were still popping."
I guess he didn't watch the safety demo where the FA clearly showed how to put two masks over one's ears...