The best scene in Terminator Genisys arrives early. Director Alan Taylor painstakingly recreates the opening scenes of James Cameron’s The Terminator, from the arrival of Arnold Schwarzenegger’s killer cyborg to the infamous moment when he confronts a group of ruffians for a change of clothes. And then something weird happens: another Terminator, also played by Schwarzenegger, shows up to fight his counterpart to the death. It’s a cool scene and its creators have divulged exactly how they pulled it off.

In a fascinating article over at EW, visual effects supervisor Sheldon Stopsack explained the three step process involved in creating a scene where a young Arnold battles his aged counterpart. The most surprising revelation is that Genisys doesn’t use a single frame of footage from the original 1984 film. Every single shot of the younger Terminator is a digital effect. And yes, you can see the seams in this computer creation when the actual fight begins, but for the most part, it’s uncanny. The static shots that recreate the original movie often look startlingly real.

The article goes on to explain the three steps required to create this digital Arnie: Finding the right body double, building the digital face, and perfecting the body language. The Cliff’s Notes version: cast Australian body builder Brett Azar as the Terminator’s stand-in, study every single Schwarzenegger movie and build a database of his facial expressions, and use the documentary Pumping Iron as a reference for Arnold’s physique.

Terminator Genisys special effects

The 35 shots of digital Schwarzenegger (about five minutes of screen time) took 12 months to complete and the visual effects team only finished 30 minutes before Taylor turned in his finished cut. But all of their hard work paid off. For all of its faults, Terminator Genisys does create a fairly incredible recreation of one of our most iconic actors. Remember the days of the terrible CGI Arnold in Terminator Salvation?

Terminator Genisys is currently in theaters. Check out the whole article at EW for many more details.