Anyone ever try to play a Jew’s Harp? The dang thing will knock your teeth out! How do you learn to play the thing without bodily harm? (Ow! That’s smarts, Babalooy!) …Maybe being toothless is the secret? - Jinx 
Draw the corners of your mouth back and pull your lips up (or down) over the edges of your teeth. Rest the Jew’s harp (or *jaw *harp, to be more PC) on your lips rather than your teeth.
You really need your teeth to get the resonance going. You know how the horizontal pieces are diamond-shaped in cross-section? Just make sure the harp rests on the very tips of the teeth, and that your teeth are on the top diamond face of the horizontals, and not extending over them.
When you master it, you can start experimenting with breathing, and changing the shape of your mouth and the position of your tongue to alter the tone. Then, like me, you’ll be maestro of an instrument that nobody in their right mind ever wants to hear played.
Ever look at a guitar player’s fingertips? Sometimes a little bodily mutilation is unavoidable while in pursuit of the great arts.
When I first started playing the Jew’s Harp* I wasn’t hurting my teeth so much as my upper lip. Whenever I would play too much the harp ended up covered in blood (which, as a teenaged boy, I thought was really cool and prooved what a hardcore instrument the Jew’s Harp was!).
