“The next time you’re on the practice tee, take a few swings and try humming to yourself while swinging. Listen to the humming.
“I hadn’t considered my swing particularly tight, but my humming told me differently. I could actually hear the tightness of my swing in the sound. While I was going back the sound would be nice and smooth, but during the change of direction my voice would become strained, and at contact my throat would constrict and the humming would increase in volume, in pitch, and most noticeably, in tightness. Sometimes, when I really went after the ball, the hum would stop after contact and I would notice that I had also cut off my follow-through. Using a tape recorder, I later recorded the sound of my practice swing and compared it with a recording of a swing at the ball. The increase in tension was painfully obvious.”
–W. Timothy Gallwey, The Inner Game of Golf