Black Sabbath’s Paranoid is such a timeless classic heavy metal anthem that it's almost possible to forget that there was a time when it was box-fresh and startling to virgin ears.For instance, when Sabbath played the Jazz Bilzen festival in Belgium on August 21, 1970, their signature song had yet to break into the UK charts, or trouble European radio airwaves, so it’s easy to imagine how confusing it was for an audience of stoned hippies gather…