I took a piece of soft plastic coming from a ring binder cover, and cut 2 parts: a circular one and a trapezoid one. Then, I made a rectangular cut in the round piece, and made a bevel on its lower edge, as a fipple.
So, I got two plastic parts and... and that's all. No glue, no adhesive tape, nothing, and the Wallet Instant Nose Flute is ready! You don't believe me? Just watch the video below.
You just have to place the smallest part (the back side of the airway) over the circular piece and, holding the ensemble like on the picture above, put your nose at the right place. There is a little knack to get not to move the small piece away from the fipple, but when you have gotten it, every attempt is a success.
Well, I deliberately chose a translucent plastic because I'm a freak, but you're not obliged to show off your nostrils like I do :)
And now, the video, for your greatest pleasure: