Nothing. There is nothing being played in reverse. I asked Lopez about it years ago. He told me to discuss it with Mike and said the answer was quite surprising. I ended up talking with Peter about it and he told me I could try asking Mike, but he's not one to really discuss the meaning behind his lyrics. So, I spoke with Mike and he said (something along these lines), "when we were recording the album at Fredmon there was another band recording at the time. We ended up picking up some weird noise through one of the mics during the process which became the intro for Demon of the Fall." I never thought to ask who was recording, but from what I was told, assuming its true, the intro to Demon is just background noise picked up during the recording.
When I asked the question to Lopez and Peter, I asked, "What was Mike saying during the intro to Demon of the Fall before the music starts?" and was told the above story. I always thought he was saying, "Help you bastard. Help me." I was shocked to find out I was way off the mark!