So yes, basically LED ZEPPELIN did 'backmask'...but were terrified of being find out...probably why PLANT says on this wiki page that he would break out into hives if he had to play that song every time they did a gig...getting found out by the ill cult presumably meant death...so when BONHAM died...they must have all heaved a sigh of relief...

http://en.wikipedia.org/wiki/Stairway_to_Heaven

Allegation of backward masking "Stairway to Heaven" (section)

The claimed backmasked section of Stairway to Heaven

In a January 1982 television program on the Trinity Broadcasting Network hosted by Paul Crouch, it was alleged that hidden messages were contained in many popular rock songs through a technique called backward masking. One example of such hidden messages that was prominently cited was in "Stairway to Heaven."[46] The alleged message, which occurs during the middle section of the song ("If there's a bustle in your hedgerow, don't be alarmed now...") when played backwards, was purported to contain the Satanic references "Here's to my sweet Satan" and "I sing because I live with Satan".[47]

Following the claims made in the television program, California assemblyman Phil Wyman proposed a state law that would require warning labels on records containing backward masking. In April 1982, the Consumer Protection and Toxic Materials Committee of the California State Assembly held a hearing on backward masking in popular music, during which "Stairway to Heaven" was played backwards. During the hearing, William Yarroll, a self-described "neuroscientific researcher", claimed that backward messages could be deciphered by the human brain.[48]

Various versions of the alleged message exist.[49] One such interpretation reads:

Oh here's to my sweet Satan.
The one whose little path would make me sad, whose power is Satan.
He will give those with him 666.
There was a little tool shed where he made us suffer, sad Satan.[50]

The band itself has for the most part ignored such claims; in response to the allegations, Swan Song Records issued the statement: "Our turntables only play in one direction—forwards". Led Zeppelin audio engineer Eddie Kramer called the allegations "totally and utterly ridiculous. Why would they want to spend so much studio time doing something so dumb?"[51] Robert Plant expressed frustration with the accusations in a 1983 interview in Musician magazine: "To me it's very sad, because 'Stairway to Heaven' was written with every best intention, and as far as reversing tapes and putting messages on the end, that's not my idea of making music."


http://en.wikipedia.org/wiki/Backmasking#Subliminal_persuasion

anyway WIKI has a whole section on BACKMASKING...but you know, it is funny but nobody even had a technical term for it...until MCDONALD figured that WIKI should have one that he made up to finger BACH...BACH-MASKING...