In fact, Manfredini has revealed in multiple interviews that he composed the now infamous whispers by slashing the words kill and mommy into two syllables ki ki ki, ma ma ma and repeating them into an Echoplex machine.
"Chi, chi, chi; ha, ha, ha?" Composer Harry Manfredini revealed that the famous refrain is actually, "Ki, ki, ki; ma, ma, ma," or "kill, kill, kill; mom, mom, mom," which is meant to represent the voice of Jason in his mother's head as she embarks on her rampage.