its sustain.
i've seen a guitar with a metal head stock. when i asked the luthier what it was all about he told me that he had been reading about the relationship between mass/sound and it was an experiment to see how it would work in an extreme example. it worked, BIG TIME sustain.
it was a little bit awkward to play and sounded a bit funny though.

thanks for the scroll in the ear tip. you might look a little funny but damned if it don't work.