A new documentary on Netflix has left viewers shaken by the subject’s inhumane, murderous behavior and the film’s graphic nature.

The three-part series “Don’t F–k With Cats,” which debuted Wednesday, chronicles the story of amateur sleuths who spent time hunting an internet killer named Luka Magnotta, a Canadian man who was captured in 2012 in Berlin after a worldwide manhunt. Then just 29, he murdered a lover with an ice pick, dismembered his body and allegedly ate parts of the victim’s corpse before shipping a hand and a foot to Canadian political offices.

But what seems to disturb viewers most — and is a nod to the documentary’s blatant title — are videos made by Magnotta and posted online in 2010. One video, titled “1 boy 2 kittens,” depicts him killing kittens by putting them in plastic bags and suffocating them by sucking out the air using a vacuum cleaner; another shows him feeding other kittens to a python.

Netflix viewers took to Twitter using a hashtag The Post can’t publish — because it uses the full expletive in the title — to describe the movie as “brutal.”

“I’ve never seen something so disturbing in all my life and I’ve watched some tough crime documentaries. what a sick individual,” one person wrote. Shocked people flooded Twitter with a deluge of superlatives, ranging from “horrific” to “f–king crazy,” and “upsetting” to “shocking.”

One Twitter user cautioned viewers to “BE WARNED before watching. I had to close my eyes & I almost threw up & I can handle watching a lot.” Another tweeter said to avoid seeing the program if you’re “triggered” by animal abuse, adding: “Didn’t realize what kind of show it was so I played a trailer — turned it off after few seconds and started crying.” And yet another viewer offered that “some of those images are going to take a long time to leave my head.”

Other viewers were disturbed that portions of the animal abuse videos were shown at all in the film. “I’m kind of angry at Netflix for using real footage of the kittens killed by that motherf–ker,” posted Twitter user @SilenceSaturne. “It was so unnecessary.”

Another person said they “had instant regrets” when they started watching. “It just took me 17 minutes to come to the complete realization and just … stop,” @rocketslifting posted.

One Twitter commenter had a vengeful reaction to the cat killer, saying the documentary is “genuinely the most f–ked up thing I’ve ever watched. Would happily slowly torture this guy til I’m satisfied he’s suffered enough like the cats he killed.”

To that end, Magnotta, now 37, was sentenced to life in prison in 2014. Three years later, he got engaged to a fellow inmate he met on a dating website for prisoners and got married the same year.