Board Thread:General MK Discussion/@comment-30202703-20160907173447/@comment-21005855-20160923140048

Actually, the original concept was meant for Mrs. Voorhees to have Jason's voice in her head. The "Chi, chi, chi, ha, ha, ha" is actually "Ki, ki, ki, ma, ma, ma" shortened for "Kill, kill, kill, mom, mom, mom". Being that this was established in the first movie (with Mrs. Voorhees as the original killer) the filmmakers kept the whispers in the sequels and remakes due to popular recognition. So really, we're both wrong.

http://www.imdb.com/title/tt0080761/trivia