The story behind Friday The 13th's "Ki ki ki, ma, ma, ma" creepy sound effect

In celebration of today, please enjoy Harry Manfedini's "Overlay of Evil/Main Title" from the score to Friday The 13th (1980). Ki ki ki, ma, ma, ma? Here's the story behind that, from Wikipedia:

Since Mrs. Voorhees, the killer in the original Friday the 13th, does not show up until the final reel of the film, Manfredini had the job of creating a score that would represent the killer in her absence.

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