[Mxsmanic]

Whenever I see those feel-good videos of famous singers banding together and
singing a cute song in order to stop world hunger, I notice that most of them
are holding their headphones with one hand. Is there a useful purpose to this,
or is it just for looks? I sometimes see music videos that look the same, with
the singer in what looks like a studio with one hand clasped against her
headphones.

Also, if a singer is wearing headphones, what does he or she hear in them? Is
it just her own voice, or a mix of everyone singing plus instruments, or what?
Why wear headphones to begin with (assuming that everyone is being recorded in
the same room)?