Lake Bell asks the person to speak in their highest note and then their lowest note and then yodel for a couple of times. Then to asks her to just speak, and the voice that comes out much closer to what we associate with a 'normal' woman's voice.
I guess having to manually change tone to such extremes resets the body's ability to recover this incredibly specific learnt behavior, and the person momentarily reverts to a clean sample of their own voice.