When I was in my twenties, I worked at a chain bookstore in a mall in Sonoma County , California. It was Christmas time, and the line of customers waiting stetched all the way through the store. People were cranky and in a hurry, and the four of us working the two registers were working as fast as we couild, but couldn't keep up. I started humming "O Holy Night" and my theatre major co-worker started singing. So I joined him, and so did some people in line. We ended up singing carols until the line was gone (hopefully not from customers :-) running in terror)As I remember, people were much less grouchy after we started singing than they had been before.