You see it wasn't actually a zombie, but a secret military program to create supersoldiers which was abandoned in the 50s because it was a failure but the disposal site leaked into a cave and gave birth to a parasisic fungus which can seeming reanimate recently deceased corpses by random triggering of the sodium- potassium pump but they aren't actually reanimated it's just random convulsions which can generate a rudimentary form of locomotion.

"Then how did the fungus respond to the Zombie's name, Scully?"

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