Just to add fuel to the fire here:
On the tune Black Dog, where Plant sings:
"Took my money, took my car, started telling her friends she's gonna be a star..."
If you reverse it says:
"ooooooooooooooHHH SATAN!"
Very distinct. Discovered it when I was 13 - slip cueing against the DJ needle on my turntable.
Now, I don't think they meant it to be there, just a trick that phonemes play, IMHO.
Dan