A neat trick

My grandmother taught me this one. First you open your mouth and say "ahhhhhh". Then, at the same time, you take your hand, fingers together, and repeatedly tap it lightly against your lips. What you should achieve is a cool, pretend Indian sound. When I first started learning this trick, my Grammom had to use her hand while I "ahhhh'ed". Now, I can do it on my own, but instead of using my fingers, I use my whole fist.