VFX Legion knows a lot about gore.

The California-based VFX house has revolted cinema-goers with a certain infamous 'rat scene' in Sinister 2 – while keeping the blood-and-guts fun and fresh in the accelerated, over-the-top action sequences of Hardcore Henry.

The team also knows how to vary the level to suit the audience, whether the teens watching supernatural TV show Hemlock Grove or the more mature viewers of FX's Justified.

You can see examples of the studio's work in their 'gore reel' below.

I spoke to VFX Legion's co-founder James David Hattin and lead compositor Kyle Spiker across a video chat. It was early morning, warm and sunny in California – for them. I'm in London where it's a gray, tepid evening and hoping that I'm not totally out of sync with them. They're friendly and relaxed, and have a genuine enthusiasm for what they do – James notes that he's wanted to create movie gore since he started mucking around with fake blood at the age of 10 (he's now 46).

However, what comes through most is their confidence and experience with blood and gore in its many shades and impacts, and that they know precisely how to get to what a director or showrunner wants.

"You've got to get the director's vision first," says James – which comes across almost as a company maxim, a corporate value for the gore industry.

Of course, matching that vision relies on the director knowing what they want – and it being communicated to those working on it. Kyle notes that he always wants to "push the envelope and then have them tell me to pull it back" – but that still relies on them knowing where that line is.

He recalls working on a pilot for a TV show whose name he doesn't disclose where they were asked to represent a sniper's bullet hitting a character's head.

"We were given no direction on gore," he says, "so I went over the top. There was brain splatter coming out and hitting the ground.

"Immediately we got feedback: 'This is a TV show. You can't have brain matter on the floor!'"

Pushing TV's boundaries

By a 'TV show', the speaker clearly meant something on network TV – as cable and streaming shows from Hannibal to The Walking Dead have shown that TV can push boundaries further than mainstream cinema. This worked in VFX Legion's favour when working on the FX crime drama Justified – which had the mix of violence and wisecracks you'd expect from being based on an Elmore Leonard story.

"There was one shot where a bad guy puts his head through a window into a bus," says Kyle. "Our hero's on the ground with a shotgun and shoots upward. It's full camera, full view. The guy falls out of the window, and the window comes down and slams.

"We tried doing a spray-misty thing. We tried keeping it TV-PG. Then, I told the artist to go with it and just go crazy. He blew the head off and threw gore up the window, which splattered everywhere. And then – when the window came down and hit – all of the pieces moved and splashed."

Despite Kyle's concerns that it might be too much even for a show on FX – the channel behind gritty, violent shows like The Shield and Sons of Anarchy – the response was positive, and influenced the tone of the show going forward.

"They loved it," he says. "They had us tone it back a little bit, and I think it lost some the secondary jitter when it hit the ground, but that set the tone for the rest of the season – and the rest of the series. It upped the game. From then on, there was more gore and more bloody hits."

Kyle is referring to how the show developed, but it could also apply to VFX Legion's work – epitomised by its work on cult action flick Hardcore Henry. It's a dumb, fun high-concept movie – with that concept being that the whole film is seen from the perspective of the protagonist (shot largely using GoPros on a custom head-rig) as he punches, kicks, shoots and slashes his way through an army of goons.

"We just went over the top," says James. "We gave a sequence to one of our artists and said, 'These guys all have to die by gunshot wounds'. He was splattering the walls with blood and everyone was spurting blood.

"That became the 'Legion style'. They would give us other sequences and they would say, 'Hey, can you do the Legion thing to this?'"

Equally bloody – but with a very different tone – was VFX Legion's work on Sinister 2. Here the gore isn't to enhance a sense of fun and excitement – it's to scare you and gross you out.

The most revolting scene VFX Legion produced for what's overall a pretty poor sequel to an inventive low-budget horror involves a family being subjected to what's known as rat torture – where rats are placed in a container placed against someone's body and the container is heated so they have to dig or eat their way through the body to escape (I write this like it's any way a normal thing to do – but variants of it are relatively common in books, films and TV shows from the Brett Easton Ellis' American Psycho to Game of Thrones).

VFX Legion's work on the scene largely comprised of combining footage of an actor on-set with a shot of a real rat eating through a form of gelatin, which had blood behind it to squirt out as the rat ate its way through. The team then layered additional blood on the shot, matching its flow to how the actor's skin stretched as they breathed and moved slightly as if in terrible pain (though tied down).

The part of the scene that really gets to Kyle though is when the rat comes out of the body, it shakes the blood out of its fur like a dog whose been in a lake.

"It's creepy," he says, imagining an audience saying 'Oh, that's juices and body stuff, it's shaking off. That's disgusting!'

One tonal difference that seperates gore in horror films from that in action flicks is the length of shot. In films like Hardcore Henry, the punch (ahem) is quick, over and done. In horror movies – or horrific scenes in other genres from dramas to war films – the camera lingers, which means VFX has to be better.

Kyle says the best results often come from a mixture of physical special effects and visual effects.

"If it's something the character is interacting with," he says, "it's usually best to suggest special effects instead of visual effects – because it looks more real. It's got the gross slimy bits."

VFX can then be used to clean up what can't be fixed on set, add additional detail and – as mentioned previously – turn up the gore (including in ways that, if attempted on set, might make retakes impossible).

As well as VFX allowing you to create the impossible, it allows for shots that are too dangerous to do on set – such as strapping a blood pack to a stuntman or actor's head for a headshot. VFX has created more than its fair share of headshots – and its gore reel is peppered with them.

Whether working with SFX or VFX, great gore doesn't mean attempting accurate realism. As Kyle points out, "a real bullet shot isn't dramatic. It's very fast and no-one sees it."

Directors often ask for shots to be 'visceral and real' and VFX Legion's job is to educate them that what they want is 'movie real' not 'real real' – as the latter can be underwhelming.

Depictions of war

The exception here is war films and TV shows, where James notes that a having soldiers just fall over due to a bullet out of nowhere is part of recreating an authentic experience. The gore happens, as in Spielberg's The Pacific, which James worked on prior to co-founding VFX Legion, when the big guns come out.

"There were loads of people's heads exploding from 50 calibre guns – brain matter flying and severed limbs," he says. "War is hell, as they say. When a grenade goes off, people start losing parts. The gore's true to life."

Even when recreating real gore, both James and Kyle emphasise that you should focus your research away from real injury and death, and not just for your own mental health. Observing how real liquids run and coalesce is essential, but stay away from the medical textbooks.

"I've seen things I'd rather not," says James, "but I don't go researching [because of that, but] because I feel like it doesn't help. The reality of it is rarely what the director is looking for. They're looking for a stylised thing, and that's going to come out of my imagination regardless.

"There's this viscous quality to the fake blood that's been around for a hundred years and nobody thinks twice about it. Blood is not viscous at all. It's a pure liquid and it moves very quickly, but we're not accustomed to seeing that on film. Rarely do we see something that is just light liquid flowing."

The art of creating 'real-looking' digital blood is recreating fake blood – which itself is a red-coloured version of the chocolate syrup from the days of black-and-white cinema. It's a simulation of a simulation, which feels real to the audience - which is what cinema is, in essence.