WATERLOO — Many people are furious after they were misled into watching a documentary about animal exploitation when they thought it would be a spooky horror flick.

A group of animal activists hosted a free mystery film screening at the Princess Twin Cinemas on Thursday after they privately rented a theatre.

The challenge targeted horror movie fanatics during their favourite time of the year, Halloween.

It was billed as the most terrifying movie to ever be shown in Waterloo. If you can sit through the end, you get a prize.

Dozens upon dozens walked out within the first 15 minutes once they found out what the movie was — a documentary about the exploitation of animals in different industries called "Earthlings."

"We felt duped," said Julia Rushton, who went to see it with a friend.

"I'm not against animal rights; it's their form of activism I have a problem with."

The activists, part of two groups known as Kitchener Ontario Animal Liberation Alliance (KOALA) and K-W Animal Save, wanted to raise awareness about animal exploitation.

Malcolm Klimowicz of KOALA said the event was a way to get people who could tolerate gory images to see the film.

"We wanted to challenge people's beliefs," he said, adding that if they told people what the movie was they didn't think anyone would come.

"We tricked people, but we also treated people."

They handed out vegan treats, gift cards and there was a $200 cash prize at the end.

"There was no false advertising," Klimowicz added.

"The surprise is that the people watching the film are the villains, instead of watching the villains on TV."

About 63 people stayed until the end of the film. It started with a full house of well over 100 people. Organizers had to turn many away.

Rushton said attendees were asked to sign consent forms while they waited in line for more than an hour to snag a seat. They asked for permission to film reactions to the scary movie.

She thought it was The Princess wanting to use footage in ads for horror films, a common promotional practice.

"It wasn't what we were there for … we didn't want to be a part of their movement."

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The collected footage from Thursday's film screening will be turned into a short documentary, Klimowicz said.

Lots of people have expressed outrage and support on social media.

One attendee, Lenny Zinger, said the film "was a fantastic way to show the public something they may have been too afraid to see before."

But not everyone agreed. Melissa Tomlin thought the Halloween hoax went too far.

She told The Record that she went to watch a fictional horror flick, not an "animal snuff film."

"I don't feel that I should be subjected to videos of animal cruelty without any warning."

Owners of The Princess did not respond to interview requests from The Record, but on Facebook it said: "I hope you can understand this was a mistake on our part. We have to screen outside groups who rent our theatre much more carefully.

"I was most concerned about how scary the movie was (graphic violence, etc.) and was assured that the movie wasn't scary and that people would be informed in advance."

Klimowicz said the cinema knew what movie they planned to screen.

"They knew all the details about what was happening."

There was a vibrant discussion after the film ended, he said.

"We knew people would be angry … but I'm really glad for the people who stayed."