Emergency Broadcast System

Preparation: A group of scouts or leaders gather in front of the scout group.

Everyone in the group hums a very high pitched note, similar to the tone on the radio just before an emergency broadcast is given.
The announcer says: "This has been a test of the Troop/Pack/Camp ____ emergency broadcast system. This has been only a test. If this had been an actual emergency, this is what you would hear"
At that point all of the group begins to scream and run around terrified and in panic, and then they all run away.