i saw a post from Muddy Pete where he found a fired shotgun shell and it reminded me of a whistle i make from hollow plant stems like mullein and sumac (not poison sumac either
first off you need to cut off the ends of the shell nice and clean. the easyest way to do that is to put a stick into it that barely fits and cut threw the plastic into the stick and roll it back and fourth till it comes off nice and clean. then you will need to make a small notch (window) about 1/2 to 3/4 inch from one end. the size is dependent of the circumference of the tube your using so you might have to experiment a little. make a plug that barely fits into the tube that stops just shy of halfway threw the window. on one side of the plug make a flat spot for air to travel. at the end that goes into the tube make an angled back cut on the plug. try to make this end of the plug sharp and clean (a hardwood stick works best) now make another plug (just make it flat, no angles or flat spots) and put it into the other side of the tube. now you need to play with the angled plug slightly by pushing it into or out of the little square window a tiny bit at a time till it starts to make a slight whistling sound. do not blow to hard. let your ears find a sweet spot. then take a stick and push the other end plug in deeper a little bit at a time while your blowing. it will take some experimenting but eventually they will both match up and create the right sized air chamber for the size of the whistle. the larger the diameter the louder it will be. the small skinny ones work good for bird calls. a larger one might make a good signaling device.
this is the mouth side plug, note the angle on the end.
the window, it might work better to make it a lille farther from the end.
the plug in the other end.
this is one i made about 12 years ago out of a sumac stalk (i think, its been a while) but any hollowed out plant with a pithy center will work.
WARNING!!!! it is up to you to know what plants are poisonous and to not use those. so pleaaaaaaaaase make sure your not using anything you don't know what it is.