I can see Doug not knowing who Fred and George are at first. However, Doug will evetually be able to tell them apart via body language, since Doug is a master of some martial arts. Of course if you go by the Quincy show(A TV show about a foresic scientist) twins are actually mirrior images of each other. One is left handed, the other right.
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Tom Mathews aka Disruptor
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Tom Mathews aka Disruptor