"I'm forever blowing bubbles..."

My voice teacher trotted out a new exercise this week.  She had me take a cup with a little water in it, along with a straw, and blow bubbles while humming up and down a fifth.  The point is to try to keep the air pressure consistent instead of letting it ebb and flow.  Not quite as easy as it sounds, but it sure does make you realize whether you're sustaining an even, level air flow.