It's Not Christmas Music Without It...

This isn't a random fact as much as it's an inquiry. I was wondering what instrument do you think just has to be in Christmas music? For me it has to be a string instrument such as a cello or violin. For someone else it may be a clarinet. My brother used to play this during our Christmas music family recitals and it probably sounded the best for Christmas music. What would be the one instrument that you just have to hear in holiday music?