The Sound of Music and the thunder sheet

My wife and I first really became acquainted when we were involved in the production of The Sound of Music while we were students at Westark Community College. If you recall, there is one scene in the movie when the children are frightened during a thunderstorm and run into Maria's room, where she sings to them, "My Favorite Things." There was a thundersheet offstage to simulate the storm, and we had a lot of fun playing with it during breaks.