One ear listening

Today, in the tube train, the woman stood in front of me was a bit unusual. She wore a hearing aid on her right ear. But when she turned her hear around, I was surprised to see that it was not another hearing aid but a headphone riding on her left ear! Since the volume is rarely quiet when listening to music in the train, isn't this habit damaging her precious and good ear? Doesn't she care?
Secretly and carefully tracing the cable line of her headphone with my eyes, I noticed that there was only one headphone. The other one bas been cut off... Oh my! her music has always been mono!!!