To add impact to a shocking moment of extreme violence, director Jim Cameron and the editors of "Terminator 2" used a very old-fashioned, low-tech editing trick.
A single frame of solid white was added into the edit precisely at the moment of impact. Nestled within a predominantly dark sequence, the quick 1/24th-of-a-second flash of bright light shocks the audience and makes the moment that much more striking.
"Mad Max 2: The Road Warrior" (1982): another example of adding a single bright frame in the middle of the edit to intensify a moment of personal violence.
Unlike the "T2" example, the frame is a single frame of overexposure (rather than a white solid color).
There's also jump cut to a different take a just before the head butt, which is hardly noticeable in real-time, especially with the added subsequent flash frame.