Composer Harry Manfredini has said the famous "Chi, chi, chi; ha, ha, ha" in the film's score is actually "Ki, k,i ki; ma, ma, ma." It is meant to resemble Jason's voice saying "Kill, kill, kill; mom, mom, mom." So if they Composer doesnt know what he writing who else?Voorhees' lines Kill her, Mommy, Kill her! and took a small sample from two words, tripled them, and gave us the infamous sound bite clip!
