Despite being Sabbath's most well-known song, Paranoid was something of a 30-minute miracle.

After initial sessions at Regent Sound in London for the album (the same studios in which the band recorded their debut) in 1970, the band moved on to Island Studios and it was during a lunch break there that Tony Iommi stayed behind to write the music that would become the band's calling card.

"He was just playing it on his own in the studio," Bill Ward told Joel McIver in an interview for his book, Sabbath Bloody Sabbath. "Geezer plugged in his bass, I sat behind my drum kit, we automatically grooved with him and Ozzy started singing. We didn't say a word to each other; we just came into the room and started playing. I think it was about 1:30 in the afternoon; Tony had the riffs, and by 2:00pm we had Paranoid exactly as you hear it on the record."

Paranoid's impact was so immediate, the band's record label Vertigo insisted that they name their second album after it, rather than War Pigs as they had planned, hence the shot of a slightly camp pink pig man with a sword on the album cover. It's a monochrome illustration on the single (above).