Ernest W. Klein, citizen of Los ANgeles, invented a new nose flute design in 1921 (application filed Apr. 23, and patent US1437317 registered nov. 28, 1922).
The shape was rather compact, even stocky, and had an interesting feature : the mouth part was shaped like a horn, in order to operate as an amplificator, and with two lip rests.
The upper lip rest is quite conventional : it's a flap coming from the mouth hole cutting out. The lower lip rest, on the other side, is a small protrusion stamped in the metal sheet.
Thus, the nose flute is absolutely hand free.
« This invention is a toy forming a whistle adapted to be held in the mouth and blown through the nose, the improved construction providing in a device of this character, improved means for properly positioning the whistle without necessitating employment of the hands, and also affording a construction in which the volume of sound produced will be amplified. »
« It will be noted that the construction, as thus set forth, provides positive means for properly positioning the horn 3 within the mouth, since the upper teeth bear against the front lip 10, while the lower teeth impinge against the rear of bead 12, and as a consequence the horn is held in the mouth by a binding engagement adapted to prevent displacement thereof, and also affording means for properly positioning the upper portion of the device over the nostrils.»
The Klein's invention has been referenced in 1992 by Ian K. Fowler, in a patent [US5165423] applied for a magnificient « Tooth Guard Whistle ».