No one knows who recorded the Wilhelm scream, but sound designer Ben Burtt coined its name based on the 1953 Charge at Feather River - the character Private Wilhelm is hit with an arrow and screams the scream. Burtt uses it a lot, but other filmmakers and sound guys have picked up on the inside joke and hide it in their movies, too. Here are 10 of them!
6. Willow uses it twice as well: when soldiers crash their carriage and when the Brownies hit some enemies with a big spears.
7. Poltergeist, sort of. Little Carol Ann is watching a war movie on T.V. and the Wilhelm occurs in that movie.
8. The Green Berets. A grenade is thrown, enemies are launched into the air, the Wilhelm is screamed.
9. Them!. Three times, actually: when ants attack the crew of the ship, when James Whitmore is killed, and when a soldier gets hit by debris in the sewer.
10. Beauty and the Beast. Chip says, "You gotta try this thing!" and then the castle is shown from the outside, where a battle ensues. A Wilhelm can be heard right after Chip's exclamation from one of the outside rioters.
And, after reading those 10 examples, you still can't quite place the scream, here it is... several times.
And, an extra bit of trivia: Ben Burtt is also the guy who created the voice of R2-D2, the sound of the lightsabers and Darth Vadar's heavy breathing (it's Burtt's own breathing in a SCUBA regulator).