Ed Golick explains something that hadn't occurred to me about that "soundie" I linked to…
The "Who's Yehudi film" was printed backwards on purpose. Panorams, the machines that showed the 16mm musical numbers, rear projected the films. If the films were printed normally the titles and the image would have been backwards. I own a number of original 16mm Panoram films and they all have reverse titles.
A little trivia. Years ago, a Yehudi radio contest was held on Bob Hope's radio program. Listeners were invited to send in who they thought the
mysterious Yehudi was. The winning entry — "Yehudi is the little man who turns out the light in the refrigerator when the door is closed."