The fact that Reese is not even remotely joking, exaggerating, or lying when he says that a Terminator will never ever everevereverEVER stop trying to kill you. No matter how badly damaged it is, it will not falter; no matter how many times you escape, it will not give up; no matter how many times you put it down, it will not despair. From its creation to its utter destruction, that thing is your death.
"It can't be bargained with. It can't be reasoned with. It doesn't feel pity, or remorse, or fear. And it absolutely will not stop, ever, until you are dead."
The beginning of the first movie, where T-800 gets into an unintentional fight with several thugs. One of them stabs the cyborg, and in response, he rips the thug's heart out, covering his left arm with blood. The surviving thug, knowing that he is next, decides to do what he is told, giving his clothes to him.
He doesn't just rip the guy's heart out T-800 grabs it and lifts the guy into the air before dropping the poor bastard.
Hell, the theme can inspire fear because there's something so primal about it. CHNKCHNK CHNK CHNKCHNK. CHNKCHNK CHNK CHNKCHNK. CHNKCHNK CHNK CHNKCHNK. CHNKCHNK CHNK CHNKCHNK.
The T-800's rampage through the police station. It really drives home how unstoppable this thing is, especially when the police break out the big guns and still get mowed down like grass.
I've always found Reese's rant to the police officers to be disturbing:
"You still don't get it. He'll find her. That's what he does. That's all he does! You can't stop him! He'll wade through you, reach down her throat and pull her fucking heart out!"
Terminator 2: Judgment Day
If you are not even marginally horrified by Sarah's nightmare, which depicts a chillingly realistic portrayal of a nuclear holocaust in Terminator 2 Judgment Day, check to see if you have a pulse.
The death of the T-1000. It was just so utterly surreal, and somehow completely lacked the satisfaction that should have come with seeing that thing killed...
Not to mention the T-1000's face turning inside-out before slowly melting away...
In-universe Fuel for T2. An escaped mental patient with a history of violence and known to have previously attacked tech companies launches an attack on one of the biggest ones. She is aided by her delinquent son and a man who matches the description of a cop killer from 1984, and is apparently immune to any conventional weapons. Not a story I'd want to be in the middle of.
The T-1000, full stop, and also doubling as Paranoia Fuel. Let's recap — it can be anyone it touches, allow it to impersonate your family and your friends to get to you. It can become other objects, so that chair or that table in the corner could well be him, and when someone sits down on it it's sampled them so now it can look like them. It can perfectly mimic human expression and emotion to blend in perfectly with normal society. It understands how to actually look for you by getting pictures and asking people where you are and searching for your personal data on computers. It understands how to manipulate people like torturing them or playing to their fears. When it finds you, it doesn't need a weapon, it is a weapon, turning its fingers and hands into knives, blades or hooks as it chases you down. Like the other Terminators, it will not stop until you are dead, and destroying it is pretty much impossible unless you have a vat of molten metal nearby. And on top of it all, he's a cop chasing a child. Able to be anyone, anywhere, without being detected, never stopping, impossible to reason with, and all it wants to do is kill you — it's about as basic and terrifying as a boogeyman can be.
Hell Is That Noise: That droning note on the soundtrack when the T-1000 is on the hunt. Whrrrr.....whrrrr....whrrr......
When the T-800 is telling Sarah and John how Skynet comes to be. The entire scene is terrifying because of how it plays on your paranoia that machines can become self aware and wipe out their creators. Plus Arnold's monotone really does make it scarier, especially when he is telling how the future will turn out bad.
Speaking of which, the T-800 running a knife along his arm so calmly before tearing it off sent chills down many a spine when it was first seen. When he runs it up his arm is the creepy part. No wonder John took Danny out of the room ...
What makes it scarier is that at first, Miles, like his wife are grossed out seeing this man before him cutting his own arm up. But upon seeing the endoskeleton arm, which looks like the exact same arm he's been studying. His look is a mix of awe from being able to see the finished result to sheer terror.
Terminator 3: Rise of the Machines
The third movie, while considered inferior by many, still has many scary scenes. One in particular: a disguised T-X is in the back seat of a police car. She makes her arm go through the driver's seat and the driver.
There's a creepy scene where Scott Mason awakens, thinking that his fiancee, Kate Brewster, is sitting on his bed. It turns out to be the T-X, who contorts her upper body to face him before murdering him. The visuals aren't perfect and there is no sound, but the scene can be found here: http://www.youtube.com/watch?v=89xKjdD8wGk
The ending of T3 gives us the rather chilling sequence of the nuclear missiles being launched on Judgment Day. With a soft violin piece playing in the background just in case the imagery wasn't enough.
The number of Jump Scares in the movie, particularly the one at the gas station. Everything suddenly goes quiet...then BOOM, a giant robotic hand smashes through the roof and grabs someone.
The thick bulky T-600s, despite being the precursor model to the T-800, are much less refined in human design. From a distance they appear human, but the simplistic rubber skin sends them right off into Uncanny Valley.
Anyone else kinda creeped out by the homage to the original films' openings with the T-800 (or whichever one looks actually human) just trudging out of the fire as John Connor repeatedly shoots it with grenades? Then there was the factory...the fact that at any moment, one of those Terminators could wake up...and then there's the one pursuing the heroes, which appears out of FREAKING NOWHERE from behind a row of moving inactive Terminators.
From the 4th movie, and also counts as Scenery Gorn — Marcus standing on a hill, overlooking a bombed out Los Angeles. Also the scene where John Connor and Marcus Wright are talking admist flaming trees. Did these guys reach into my childhood nightmares or what?
When Marcus finds out the hard way that he himself is a terminator. This is a guy who is atoning for the deaths he caused prior to his execution. A guy who until meeting John Conner was protecting Kyle Reese and Star before their capture, fighting machines trying to kill them. Then he finds out that he is one of them. A machine whose only purpose is extermination.
The revelation that in Salvation, nowhere is safe from Skynet. Even when John's helicopter crashes into a river near the Resistance base as they chase Marcus and Williams, you'd think "Oh, they just need to swim out, no big deal." WRONG. The water is crawling with a horde of swimming robots, and we get to see them drag John's screaming copilot underwater and filet him.
One could be forgiven for thinking that John Connor had his T-800 problem licked in Salvation when he caused molten metal to be poured upon it. However, this only slows it down. After it has fully risen, the T-800 looks like the Grim Reaper, with the only difference being that its hooded robe is composed of molten metal.