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South African sprinter Oscar Pistorius claims he mistook his girlfriend for an intruder after waking during the night. He shot her to death through a bathroom door. It wasn’t until after the lethal shots were fired, says Pistorius, that he realized Reeva Steenkamp was not in bed. It will be up to the court to determine whether Pistorius’ story is true. But in general, why are people confused when they first wake up?