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. Manfredini was inspired by the 1975 film Jaws, where the shark is not seen for the majority of the film, but the motif created by John Williams cued the audience as to when the shark was present during scenes and unseen. While listening to a piece of Krzysztof Penderecki music, which contained a chorus with "striking pronunciations", Manfredini was inspired to recreate a similar sound for Friday the 13th. He came up with the sound "ki ki ki, ma ma ma", based on the line "Kill her mommy!", which Mrs. Voorhees recites repeatedly in the final reel. The "ki" comes from "kill", and the "ma" from "mommy". To achieve the unique sound he wanted for the film, Manfredini spoke the two words "harshly, distinctly, and rhythmically into a microphone" and ran them into an echo reverberation machine. Manfredini finished the original score after a few weeks and recorded it in a friend's basement. [The film's writer] Victor Miller and assistant editor Jay Keuper have commented on how memorable the music is, with Keuper describing it as "iconographic". Manfredini makes note of the mispronunciation of the sounds: "Everybody thinks it's cha, cha, cha. I'm like, 'Cha, cha, cha'? What are you talking about?"