Since it was first published in April 1979, the beloved children's classic Bunnicula—about a vampire bunny who sucks veggies dry, turning them white, and the cat and dog who try to expose him—has sold more than 8 million copies, won a number of awards, and spawned a couple of cartoons. Here are a few things you might not have known about the book.

1. James Howe was a struggling actor when he came up with the idea for Bunnicula.

“I was doing what a lot of actors do and staying up too late and watching movies on TV,” Howe told Book Page in 2011. “It was watching all those bad vampire movies in the '70s that led to the idea of Bunnicula.” Howe told Scholastic that many of the movies were more silly than scary. “I don't remember the moment when the character Bunnicula came into my head,” he said. “I suspect it came from asking the question, what's the silliest, least likely vampire I can imagine?”

2. His mother-in-law suggested writing a book about Bunnicula.

After he came up with the character he called “Count Bunnicula,” Howe made “a little greeting card … of a vampire rabbit,” he told Teaching Books—but he never thought about writing a book featuring the character.

“I was not writing then—even though I always loved to write, I wasn’t thinking of it as my work,” he told NPR. “It was actually [my wife] Debbie’s mother who said, ‘That would make a great character for a children’s book. Why don’t you two try that?”

So one night after dinner, just for fun, the Howes started writing the book that would become Bunnicula: A Rabbit Tale of Mystery. “One of us would hold the pad of paper and essentially be secretary,” Howe said. “We wrote that book completely out loud—we told the story; one of us would begin a sentence, and the other one might jump in and finish the sentence.”

3. The opening sentence of Bunnicula never changed.

“The final, published story is essentially there in the first draft, just as we told it,” Howe told Teaching Books. “In fact, it only took maybe three or four drafts, and mostly that was fixing and polishing.” From the time the Howes sat down to write until the time Bunnicula was published, the very first sentence, spoken by Harold the dog—“I shall never forget the first time I laid these now tired old eyes on our visitor”—never changed.

4. Debbie died before Bunnicula was published.

Several months into writing Bunnicula, Debbie was diagnosed with cancer. At first, Howe said, they put the book aside. “We had other things to deal with,” he told Teaching Books. “But, after a few months, we needed to laugh. We needed something to put our minds to that wasn't so serious and difficult, and we went back to writing Bunnicula. Writing that book really made us laugh; it served the greater purpose of easing the pain and lifting our spirits.”

Sadly, Debbie wouldn’t live to see the book in print. She passed away in June 1978 at 31; Bunnicula was published the next year.

5. The most challenging Bunnicula illustration for artist Alan Daniel was the first one.

When illustrator Alan Daniel—who has created art for books like Fireside Al’s Treasury of Christmas Stories, Get Out of Bed!, and The Best Figure Skater in the Whole Wide World—received the Bunnicula manuscript from his agent in 1978, “I laughed all the way through it,” he told Mental Floss in an email, “and could hardly wait to get to work.” When he got down to drawing, “I would be so deeply into what I was doing that my children would come into my studio and see the expression of the character I was drawing reflected in my face.”

He received no art direction. “All the information on the characters is implicit in the text, which I read carefully several times,” he said. So when choosing which scenes to illustrate, Daniel looked for dynamic situations. “I want to show all the characters and make sure the pictures are well placed throughout—not bunched up,” he said. “The story is told from the animals’ point of view so the illustrations are also from that POV. The family is part of the animals’ world so they need to be there, but they only appear twice.”

The most challenging illustration to create, he said, was the first major one: “It is a dark and stormy night so the lighting is tricky. Bunnicula is just a pair of eyes within a dark bundle. A lot had to be established in that illustration. I wanted to present a world that was real so the fantastical elements of the text could play against it.”

Daniel used three different pencils to create the illustrations. An HB graphite pencil got the most use. A 2H pencil “let me get a grayer look for things I wanted to recede,” Daniel said, while “2B gave me real darks. Everything was built up with fine lines except the chair for which I used the texture of the illustration board. Having a full-color cover was a challenge because I wanted to keep the look of the inside pictures. I used muted watercolor over pencil.”

He said that even decades years after the initial publication, “[people] come and tell me stories about their discovery of the book.”

6. Acceptance was an accidental theme of the first Bunnicula book.

“Writers are drawn to themes that we write about, but we don't necessarily know what they are,” Howe told Teaching Tolerance magazine in 2006. Howe didn’t know what his theme was until a fourth grade student wrote to him after Bunnicula was published. “In the book, a strange rabbit is suspected of being a vegetarian vampire after he comes into the home of, in my view, a typical suburban family,” he said. “This girl wrote, ‘I learned from this book to be accepting of someone who's different. Harold just accepted Bunnicula. He said, He's different. So what? Chester was suspicious of him and wanted to destroy him.’ There it was. There was my theme.”

Howe also related this story to Scholastic, saying that acceptance has “become a theme in much of my work and it's interesting that it might have unintentionally been a theme in my first book.”

7. The first Bunnicula sequel was inspired by Agatha Christie ...

When it came time to write a sequel to Bunnicula, Howe had a bit of trouble. He told Scholastic that, with his initial sequel idea: “I felt I was rewriting Bunnicula itself, so I knew I needed to make a big change somehow. I asked myself where else could animals go to have an adventure if they didn't stay at home? One of the first thoughts I had was a boarding kennel. As soon as I thought of a boarding kennel, I thought of the mysteries of Agatha Christie, where often a group of strangers come together in a holiday setting, one of the guests is murdered and the other guests become suspects. That gave me my basic plot structure for Howliday Inn.” It was published in 1982.

The initial idea he’d been trying to write would become the second sequel, The Celery Stalks at Midnight (1983), which was inspired by a friend who wondered if the vegetables Bunnicula drained also became vampires. There were four other Bunnicula sequels: Nighty Nightmare (1987), Return to Howliday Inn (1992), Bunnicula Strikes Again! (1999), and Bunnicula Meets Edgar Allan Crow (2006).

8. … But there's some Sherlock Holmes in the Bunnicula books, too.

“As much as I was influenced by vampire movies in writing them, I was also influenced by watching a lot of Sherlock Holmes movies,” Howe told Teaching Books. “It took me a while to realize this, but Chester is Sherlock Holmes and Harold is Watson, and they are kind of bumbling detectives who try to figure things out.”

9. Bunnicula was adapted into two musicals ...

Jon Klein adapted the book into a musical for Seattle Children’s Theater in 1996; music was composed by Chris Jeffries. Since its debut, Bunnicula the Musical has been performed around the country. Another musical called Bunnicula: A Rabbit Tale of Musical Mystery featured a book by Tony nominee Charles Busch, with music by Sam Davis and lyrics by Mark Waldrop. It played off-Broadway in 2013.

10. … And an animated Bunnicula special.

Bunnicula: The Vampire Rabbit debuted in 1982 as part of ABC’s Weekend Specials. The 23-minute film was directed by Charles A. Nichols, who had previously served as animation director on series like Scooby Doo, Where Are You! and Josie and the Pussycats; he would go on to direct episodes of Alvin and the Chipmunks.

11. There were other Bunnicula books, too.

Bunnicula spawned two spin-off series: Tales from the House of Bunnicula, whose books were narrated by dachshund puppy Howie (he made his debut in Howliday Inn), and six oversized picture books called Harold & Chester. There was an activity book, written by Howe and illustrated by Alan Daniel, which contained stickers, puzzles, riddles, and word games; it was published in 1993. Bunnicula's Frightfully Fabulous Factoids: A Book to Entertain Your Brain! was published in 1999, and in 2005, Bunnicula and Friends—simplified versions of the books for early readers—debuted.

12. Howe's favorite Bunnicula character was Harold.

When Scholastic asked Howe who his favorite character was, he chose Bunnicula's canine narrator. “I would have to say Harold because I'm closest to him since I write as him,” he said. “But in the series I also really enjoy writing Howie.”

13. The Monroe family never found out about Bunnicula.

“They remain in the dark the whole time,” Howe told NPR. “They just think their pets act very strangely at times, as we all do.”

14. Bill Hader was a big Bunnicula fan.

“The first series I was obsessed with was James Howe’s Bunnicula,” Hader told The New York Times. “I read all of those.”

15. There's another cartoon based on the Bunnicula book.

Bunnicula, which debuted on the Cartoon Network and Boomerang in 2016, does away with the Monroes and Howie completely. Instead, the show follows a girl named Mina and her two pets, Chester (Sean Astin) and Harold (Brian Kimmet), who discover Bunnicula (Chris Kattan) after they move to an apartment in New Orleans, left to Mina’s dad by a mysterious aunt.

It’s different from the books, but Howe was apparently OK with the changes. “The only thing he really wanted was for us was to be true to the characters,” producer Jessica Borutski told TV Insider. “Bunnicula’s very different, but he wanted us to stay true to Chester and Harold and honor their personality types. That’s what we did.”