Stairway to Heaven Backwards?

Okay, I suppose we all know what happens when you listen to Stairway to Heaven backwards. In case you don't: you're supposed to hear these crazy backwards messages. You can look it up on YouTube. Anyhow, I was curious: it works when you listen to the studio version of the song, song by Led Zeppelin (Robert Plant, actually, but hey - that's not exactly important right now). Why not if you sing it yourself?

So that's what I tried. Using the audio editor program Audacity, I recorded myself singing the lyrics to Stairway to Heaven, except I didn't slur my words like Robert Plant does in the recording. Ever noticed how he always seems to slur his words weirdly on those Zeppelin recordings, eh? Well, I sang the words correctly, and I discovered that I could just barely hear some of it. But otherwise, I could hear none of it. Badgers, I don't know what this means. I guess that all we can gather from this is that it doesn't work when  you use proper pronunciation.