On our 5/6 Water Sentinels outing, the kids spotted a lovely bull snake in the grass. Bull snakes mimic rattle snakes as a defensive mechanism even though they are not venomous -- they have similar patterning, will coil, will flatten and broaden their heads to look like a viper, and will shake their tail. But they have no rattle so they make their rattling sound by forcing air through a small opening just behind the tongue, causing the surrounding tissue to flap around. Gladly, we didn't get this particular snake sufficiently addled to put on such a display.
Providing free nature outings and adventures to youth who would other wise not have such opportunities, Boulder Valley ICO is entirely volunteer run.