The next problem was making a 36-year-old bodybuilder move as though a computer—not a human nervous system—controlled every action.

PART 2 — HOW THE LUNCH CHANGED THE MOVIE

Once Schwarzenegger accepted the Terminator role, the discussion from lunch stopped being theory. He now had to make those ideas visible on camera. That meant removing many of the small behaviors actors normally use to make a character feel alive.

Schwarzenegger later explained that he practiced handling weapons until the movements could be performed without looking down. The Terminator should not search for a magazine, check where a control was located, or hesitate while operating a gun. A computer inside the machine would already know where everything was. He also practiced firing without blinking. Human beings instinctively react to noise, recoil, muzzle flash, and nearby explosions. The Terminator was not supposed to react because none of those things surprised it. (Men's Health)

The rule extended beyond gun handling. A conventional villain might smile after gaining an advantage or show irritation when a victim escapes. Cameron’s machine would not. Failure simply generated another action. A locked door became something to pass through. A wounded body became damaged hardware. A police station full of officers became an obstacle between the machine and Sarah Connor. The Terminator did not become angrier as the story progressed because anger would imply an emotional life it did not possess.