Look up, it's 1951 and this is "Distant Drums" [The Movie]. "Unnamed Soldier" is crossing a swamp amongst several of his comrades, in pursuit of Seminole Indians. Sun hot upon cheek, mind set to purpose, he is doing his best to keep up when suddenly, he feels something move underneath him. Last thing he does is let out a loud shriek of agony as he is dragged down and under by "random alligator".
Skip now to 1953 and behold Private Wilhelm in The Charge at Feather River, struck by random arrow. Surprised and in pain, Wilhelm wales into the wind; a sudden piercing shriek oddly resembling that of "Unnamed Soldier" from two (2) years back.
You have just been witness to the origins of The Wilhelm Scream, a sound effect that will go on to be heard by billions of moviegoers the world over.