On January 7th, 1971, Black Sabbath released their second album, Paranoid, in America. To celebrate the set’s anniversary in the States, here are 20 things you might not know about it:

1. The band started working on Paranoid just four months after the release of their self-titled debut.

2. The group’s writing process started with guitarist Tony Iommi playing a riff, Ozzy Osbourne creating a melody, bassist Geezer Butler doing the lyrics and drummer Bill Ward setting the beat.

3. Many of the songs started from music that came from the band’s onstage improvisational jams.

4. Sabbath planned to call the album War Pigs but their label allegedly feared backlash from Vietnam War supporters. They also thought “Paranoid” would be a better single than “War Pigs.”

5. While the group changed the album name to “Paranoid,” they didn’t alter the cover art, which shows a pig with a sword.

6. The original UK gatefold sleeve featured a black and white photo of the band on a grassy hill. It marked the group members’ first appearance in album art.

7. “War Pigs” was originally called “Walpurgis,” the Satanic version of Christmas, because Geezer thought war was like Satan since it is only about evil.

8. The addition of the air-raid siren in “War Pigs,” and the speeding up of the song at the end, were the work of the album’s producer and engineer. The band had no input in the decision, but they liked it.

9. The title track was actually done after the band thought they completed the album. They didn’t have enough songs so Tony played the lick for “Paranoid” and 25 minutes later they had the track.

10. Geezer wrote “Paranoid” about depression since he didn’t know the difference between depression and paranoia.

11. Butler was against “Paranoid” being on the album because he thought it sounded too much like Led Zeppelin’s “Communication Breakdown.”

12. “Paranoid” is the Finnish equivalent of “Free Bird” – audiences loves to request the track at all sorts of concerts. To do it they yell, “’Soittakaa Paranoid!’” or “play ‘Paranoid.’”

13. “Iron Man” was originally called “Iron Bloke.” Ozzy came up with it after saying the track sounded “like a big iron bloke walking around.” They later changed it to “Iron Man.”

14. “Iron Man” doesn’t have anything to do with the Marvel Comics superhero, but they have become associated since the song was used in the 2008 film Iron Man.

15. Because of how quiet “Planet Caravan” is, the group had doubts about including it, but they liked how it was like a love song only instead of normal romance, it was about taking a spaceship out to the stars.

16. “Hand of Doom” came about after the band members observed American soldiers who returned from Vietnam and struggled with drugs in the UK, namely heroin.

17. When the band was playing massive sets in Europe that were hours long, Bill would do 45 minutes on his own with a drum solo. That led to the Paranoid instrumental “Rat Salad.”

18. Geezer once said that “Fairies Wear Boots” was inspired by a bad encounter that Ozzy had with skinheads, but Tony claims it came from a time when Geezer and Ozzy were smoking pot and saw fairies in boots running around a park.

19. The intro to “Fairies Wear Boots” is called “Jack the Stripper.”

20. Paranoid is Sabbath’s best selling album, having moved more than 4 million copies in America.