They did that in the Bahnson experiment. What it shows is visible reed action inside the harmonica. All you can see of Howard's body is a little bit of lip and maybe tongue tip - not enough to get any idea what he's doing to make a bend happen - that's where the ultrasound comes in.
Winslow
Winslow Yerxa Author, Harmonica For Dummies ISBN 978-0-470-33729-5