At the Bushcraftfestival Harry Sepp demonstrated how to make a whistle from a drinks can. Mors Kochanski taught me this when I was in Canada, so I thought I would re-post the how-to that I wrote ten years ago;
Cut a strip from the side of the can about 20mm wide and break off one third of this strip as shown below.
Bend the short piece into the shape of a hill and place across the longer piece a few millimetres from one end forming the mouth piece.
Fold one end of the long piece and both ends of the short piece to secure in place as shown below.
Now bend the long piece at a ninety degree angle to the mouth piece and then curl it around to form the air chamber and you should have a shape rather like a question mark.
Place your thumb over one side of the air chamber to form a seal and your index finger to seal the other side, just leaving the narrow opening immediately after the mouth piece.Ensure the gap at the front of the mouth piece is wider than that at the back (this will take some adjustment and experimentation to get right), then blow!
While I was at the festival, Paul Kirtley did a Podcast interview with myself and some of the other attendees, and this podcast is now available to listen to here;