How do you tune a sherbet container?

Peter Mayer and friends recently performed at Smoke Rise Baptist Church in Stone Mountain for a stop on the 2009 Stars and Promises tour. One song, Junkman's Christmas, involves the musicians using discarded, old or make-do instruments, just as a junkman would. At one point, Mark Holland, a brilliant performer on Native American flutes, picks up a Prairie Farms Natural Fruit container and blows bubbles along with the music. Funny thing is, it seemed to fit in nicely.

Poor picture quality, but you get the idea.