Concept Album: Metal band Trick or Treat recorded a double album retelling the story, titled Rabbit's Hill.
Executive Meddling: Sort of. According toWord of God, Bigwig really should have succumbed to his wounds after the fight with Woundwort, but the author's kids wouldn't stand for that.
Genre Popularizer: There are a number of other "epic animal adventure" Xenofiction stories, but it is difficult to read them without comparing them to Watership.
The Russian video game Metro Exodus has a brief scene with two rabbits floating down a river on a raft. Video here.
The band Fall of Efrafa took their name from the totalitarian warren in Watership Down and references to the book are rife throughout their lyrics and artwork.
Advance of Zeta: Flag of the Titans has a massive number of references to the book. The book focuses on the Titans Test Team, whose various emblems are rabbits. Many of their Mobile Suits are named after the characters — for instance, the initial Gundam that shows up, the RX-121 Gundam TR-1 is nicknamed "Hazel" while its final form, the RX-121-C3 is nicknamed "Haze'n-thley", named after Hyzenthlay. The spinoff books continue this trend.
Spared by the Cut: Bigwig was supposed to die after he fought Woundwort. After Richard Adams' daughters begged him to spare him, he changed his mind.
Write Who You Know: Kehaar was based on a Norwegian Resistance Fighter, and the rabbits that Hazel leads from the Sandleford warren are based on members of Richard Adams' unit in World War II, with Bigwig and Hazel in particular based on specific individuals.
Written for My Kids: The book was first made up by Richard Adams as a story to tell his two daughters while he was driving them in his car. It was the daughters who persuaded him to later write the story down.
For the Film:
Box Office Bomb: Though successful in the UK, the film underperformed in the US, earning under budget ($3.7 million against $4.8 million). It was mainly because of being released the same month as Halloween.
Cut Song: Mike Batt wrote and recorded three songs with Art Garfunkel for the film, but only "Bright Eyes" was used.
Deleted Scene: According to composer Angela Morley, a scene where Dandelion tells the others the story of King Darzin was cut due to Martin Rosen feeling it slowed the film's pace down. The film's music cue sheets show that the scene originally took place when the rabbits are at Cowslip's warren, and presumably would have followed straight on from when Hazel prompts Dandelion to tell them a story.
The Film of the Book was to have been directed by John Hubley, but he died early in production and was replaced by Martin Rosen. Some of his work, such as the opening scene, remains in the finished film.
Zero Mostel passed away before the film was released.
Disowned Adaptation: Richard Adams had very little creative input in the adaptation and, while he thinks the film is good on its own merits, dislikes how much is lost in adaptation and overall prefers that people who see the film at least seek out the books afterwards.
Keep Circulating the Tapes: The soundtrack's release was very limited, and only recently has a digital release come.
Posthumous Credit: In Zero Mostel's final film role, he recorded his parts before passing away suddenly from what has been assumed to be an aneurysm, and the film was released after his passing.
Technology Marches On: Over 40 years later, the animated film has aged surprisingly well. Because of the lack of focus on humans and all the tech you see them using (shotguns, cars), this story could have been set in the 2020s and it would still essentially look the same. For all you know the humans have smartphones and are on the Internet in the house.
At one point, George Martin was approached to compose the film's score while America, who Martin was producing at the time, were to provide a theme song, but ultimately these plans fell through. By that point the proposed theme song by America had already been written, so rather than waste it they just included it on their next album.
Word of God, Bigwig really should have succumbed to his wounds after the fight with Woundwort, but the author's kids wouldn't stand for that.