When the back masking hype was at it's greatest, I recall a Christian band (Petra, I think) started a song with what sounded like nonsense. Play it backwards and it apparently clearly said "Why are you looking for the Devil when you should be looking for the Lord"!

Can't recall the name of the song.
All of the supposed instances of back masking have never been technically verifiable; that is, if you play the bit backwards through a synthesizer, it's not recognised it as human speech or voice. The doomsayers say it's because satanic voices aren't human.

I say it's because a mechanical device doesn't extrapolate like our brains do.
Cheers
Mick