In a movie filled with complex and groundbreaking CGI, this scene, ultimately cut from The Terminator 2, is still impressive. Warning, a small amount of fake blood and cutting skin:
The clip is old, but if you haven’t seen it, notice how the mirror is used. Connor is cutting into and removing something from the head of the Terminator, but obviously they couldn’t have Linda Hamilton actually cutting into Arnold Schwarzenegger’s head.
If you don’t know how the effect was done without CGI, watch it and think about it.
The effect was done without a mirror, using Leslie Hamilton in the “mirror” together with Schwarzenegger, while Linda Hamilton is cutting into a dummy, made up to look like Schwarzenegger, synchronising their movements.
Leslie also appears in the dream sequence, as the T-1000 disguised as Connor and as the day-dream at the end.