I mean split mind.
Loudermilk: I mean split mind. This monster isn't David. It's a parasite of some kind. You see, another consciousness inside him.
Melanie: What does that mean?
Loudermilk: This thing burrowed into David's brain when he was a boy, maybe even a baby, and has been there, feeding off him ever since.
Ptonomy: The memories?
Loudermilk: Memories, exactly! Every time David sees this thing, or realizes it's there, this creature makes him forget-rewrites his memory.
Melanie: Is that why we couldn't see it?
Loudermilk: I think so.