Hehe thanks. Yes it could well be a headworm or an earworm - and yes, I am now humming that Christmas song four months early!

After thinking about it, I think the idea (the head part at least) might have come from seeing Jacob Epstein’s sculpture ‘Rock Drill' as a small lad. According to wikipedia the sculpture may have influenced the creation of the Star Wars character General Grievous.

https://en.wikipedia.org/wiki/Rock_D...Jacob_Epstein)