WTF? How Could This Be?

Someone observed a strange phenomenon and wanted an answer:

Every once in a while, my eighth-inch audio jack will slip loose and I'll seemingly lose only the voice part of a track -- leaving somewhat of a "karaoke" version. What I would guess about how audio plugs work suggests that I'd be making this up; however, I've asked and others tell me they've experienced this as well.

What causes this stripped vocals from audio when a 1/8' audio jack is partially unplugged?

The author of this question couldn't believe this was happening himself.  But I can easily imagine observing this myself, and becoming obsessed with getting an answer to this unexplainable, but repeatable, observation.  It's a bit like walking outside and seeing your car floating three feet in the air – but only when you've accidentally left your front door ajar on your way out.

Naturally, our geeky questioner went to the best crowd-sourcing site around for answering questions on electronics: Electronics StackExchange.  And they got an answer – a sensible, plausible, clever, and unexpected answer.  Go there and read the first answer on this post – it's a classic...