Nearly 10 years ago, Werner Herzog returned to nonfiction with a streak of documentaries focused on Tibetan Buddhism, aviation, the oldest art known to man, and people living in unique extremes. Grizzly Man, a film about amateur naturalist Timothy Treadwell’s life (and death) with bears, was at the center of this explosion of real-life stories.

Treadwell spent 13 summers living among the bears in Alaska’s Katmai National Park and Preserve, filming footage and styling himself as a rogue protector who could get close enough to the grizzlies to pet them. In 2003, he and girlfriend Amie Huguenard stayed past the summer into the pre-hibernation season. Eventually a bear mauled them both, leaving behind the footage and a lot of questions which Herzog mined for his film. Here are 10 things you might not know about Grizzly Man, which was co-shot by its subject.

1. A PAIR OF MISPLACED GLASSES LED WERNER HERZOG TO THE DIRECTOR'S CHAIR.

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The German auteur was in the office of Erik Nelson, who produces projects for National Geographic and Discovery, hunting through his pockets and a bunch of papers on Nelson’s table for his reading glasses when an article about Timothy Treadwell caught his eye. Nelson encouraged him to read it because they were going to make a movie about it.

"So I read it and immediately hurried back to his office, and I asked, 'Who is directing it?,'" Herzog told NPR. "And he said, 'I'm kind of directing it.'  And there was some sort of hesitation, and with my thick German accent I said, 'No, I will direct this movie.' And that was it. We shook hands and I made it."

2. TIMOTHY TREADWELL SPENT 35,000 HOURS WITH THE BEARS.

Many viewers were critical of Treadwell, particularly for familiarizing bears with a human presence in a way that could potentially lead them to lose their fear for both poachers and campers. However, noted bear expert Charlie Russell defended Treadwell, particularly his innate way of connecting with the bears and the dedication it took to spend 35,000 hours over 13 years with the animals.

3. TREADWELL WAS HOPING TO TURN HIS FOOTAGE INTO HIS OWN MOVIE.

Herzog started with 100-plus hours of footage Treadwell shot of his time in the park. Besides the enormous amount of film, it was all meticulously curated both in how it was shot and in what takes were kept. As Grizzly Man points out, “Treadwell” was a stage name for the aspiring actor who lost out on a role on Cheers (he claimed to come very close to landing the part of Woody Boyd) and captured his encounters with the bears as a nature documentary host. He released an hour-long edit of footage that Herzog saw during production but kept almost all of the footage within his circle of friends.

4. DAVID LETTERMAN JOKINGLY ASKED TREADWELL IF HE THOUGHT HE'D BE KILLED BY A BEAR.

The only part of the documentary that was replaced or edited out was a segment of Late Show with David Letterman where the host pointed out the obvious: the risk Treadwell was taking. Treadwell responded that he wouldn't be killed by a bear, echoing an ironic sentiment at the beginning of the doc where he claims there’s no real danger of that happening.

5. HERZOG WAS SURPRISED BY THE INTENSITY OF TREADWELL’S FOOTAGE.

The director and his team went through the massive amount of footage Treadwell shot to transform 100-plus hours into a 103-minute documentary (and to plan their own footage and narration). Herzog found the intensity of the footage “unexpected.”

“It was always clear to me that it wouldn’t be a film on wild nature, that it would be much more a film on our nature,” Herzog told CHUD.com. “Treadwell is a very complex character full of doubts and self-aggrandization. Full of demons that haunt him and exhilarations and swings in mood, and seeing a mission that he finds himself into, and being almost paranoid for moments, and being very sane and very clear at others.”

6. HERZOG NEVER PLANNED TO USE THE FOOTAGE OF TIMOTHY AND AMIE’S DEATH.

It was known before Herzog made the documentary that Treadwell’s camera had captured audio of his and Huguenard’s deaths, so Herzog couldn’t avoid it. After filming himself listening to the footage in front of Treadwell’s friend Jewel Palovak, Herzog immediately decided that he wouldn’t use the footage itself in the film, both out of respect for the dead and to avoid making what he called “a snuff film.”

7. HERZOG REGRETS TELLING JEWEL PALOVAK TO DESTROY THE TAPE.

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Herzog's gut reaction to listening to the audio was to tell Palovak to get rid of the tapes. “But that was stupid,” he later told Paste. “Silly advice born out of the immediate shock of hearing—I mean, it’s the most terrifying thing I’ve ever heard in my life.” Palovak placed it in a bank vault instead.

8. AMIE HUGUENARD’S FAMILY REFUSED TO TAKE PART IN THE FILM.

The documentary features interviews with Treadwell’s friends, but Huguenard’s family is noticeably missing. Their refusal wasn’t out of malice specifically to Herzog’s project, though. They decided not to speak publicly in any way about Amie’s death.

9. THE MOVIE ISN’T ABOUT BEARS BEING DANGEROUS.

The ultimate message of the movie is easy to miss because Treadwell’s death looms so largely—suggesting that he was wrong about bears being safe. Except even Herzog was intent on repeating how safe they are. “Sure, you are in a certain danger, but we should not exaggerate the danger,” Herzog said. “Grizzly bears normally do not kill and attack human beings. It doesn’t happen very often. Statistics are clear since 1903 or so, there were statistics in Alaska, and more than a hundred years, not more than 12 or 14 people got killed by grizzly bears.” Herzog’s point is that Treadwell wrongly believed that nature could be tamed.

10. TREADWELL’S FRIENDS THOUGHT HE COULD DIE IN ALASKA, BUT NOT BY BEAR ATTACK.

Herzog noted that Treadwell repeatedly broached a desire to die during a fight with a bear but didn’t think a bear would kill him. His friends thought he was safe with the bears, too. “I thought he might get hurt, fall on rocks and break something, drink tainted water, but I never believed he would be killed by the bears,” Palovak said.