Cyborgs don't feel pain.

Reese: "Cyborgs don't feel pain. I do. Don't do that again." Sarah: "Just let me go." Reese: "Listen and understand! That terminator is out there. 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."