
Other mistake: Truck chase scene, the driver-side fender changes color. Starts as red then changes to blue. (00:18:27 - 00:20:10)

Continuity mistake: When John is killed, the stool on the right moves away between shots.

Revealing mistake: In Guatemala, when Arnie shoots John, in the shots from behind Arnie's body double is noticeable.
Answer: Skynet and Legion were both developed for identical purposes: defense network artificial intelligence. It stands to reason they would both evolve in similar ways. Since both Skynet and Legion were fighting a similar human resistance, they both developed similar infiltration units.
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