Make a Pill Bottle Caller
A tube caller can easily be fashioned from a plastic pill bottle. A snap-on lid works best.
1) Use a sharp knife to cut a half moon shape through the lid.
2) Turn the bottle over and cut a small hole into the bottom. It can be made with a hot knife point or ice pick. The larger the hole, the greater the volume.
3) Cut a piece of thin balloon or latex and place it over the open end of the bottle. Replace the lid, making sure the straight edge of the rubber is aligned with the cut edge of the lid.
Tone is varied by increasing or decreasing the tension of the latex. To make it yelp, place your lower lip against the rim of the lid, with your upper lip barely touching the rubber. Exhale sharply on the rubber to make it vibrate.