Director Zack Snyder (Batman v Superman: Dawn of Justice, Man of Steel) just released a new four-minute short film. It’s called Snow Steam Iron, and if you want to watch it, you’ll have to download an app first. The app, Vero, is pitched as a social network for creators; Snyder has used it in the past to share Justice League footage.

Here is the synopsis of Snow Steam Iron, according to Vero: “Snow gently falls on the blood-stained streets of a seedy out-of-time New York City. Steam envelopes the nightmare unfolding within its narrow alleys. Iron is the will of the one who would dare to resist… fight… survive.”

Snyder made the film with the help of his son and daughter, according to an interview with Wired. “It was a cathartic experience for all of us in a weird way because when we all get together it’s easier for us to make a movie than talk,” he said. Snyder stepped down as the Justice League director following a family tragedy earlier this year, and was replaced by Avengers director Joss Whedon.

Snyder shot Snow Steam Iron entirely on an iPhone — a technique that has been used by directors for years now, like in Sean Baker’s 2015 Sundance breakout Tangerine and Adam Green’s 2011 film The Wrong Ferrari.

The iPhone constraint clearly had little affect on Snyder’s hallmark aesthetic: the short is violent, stylized, and uses slow-mo generously. A word of warning to those at work: there is some nudity.