Found by my son Nic on Wikipedia:
The Wilhelm scream is a frequently-used film and television stock sound effect first used in 1951 for the film Distant Drums. The effect gained new popularity (its use often becoming an in-joke) after it was used in Star Wars and many other blockbuster films as well as television programs and video games. The scream is often used when someone is pierced with an arrow, falls to his death from a great height, or is thrown from an explosion.
The Wilhelm scream has become a well-known cinematic sound clichÃ©, and is claimed to have been used in over 216 films
By the way, Nic thanks everyone for their help on his blog and his writing project. He is writing a novel over the next year, dealing mixing his interest in sports with dystopian themes. This entry into the Hayek poster contest actually comes really close to the themes in his book. I thought he was getting on a wrong track by trying to use Atlas Shrugged too much as a model. While I love the book and it has had a profound effect on me, as a work of fiction it is pretty limited, with black and white characters and no character movement/development at all. I am making him read the Fountainhead right now as a better example of having more intriguing characters.