COBB: What's the most resilient parasite? A bacteria? A virus? An intestinal worm?
ARTHUR: What Mr. Cobb is trying to say-
COBB: An idea. Resilient, highly contagious. Once an idea's taken hold in the brain it's almost impossible to eradicate. A person can cover it up, ignore it- but it stays there.
SAITO: But surely-to forget...?
COBB: Information, yes. But an idea? Fully formed, understood? That sticks... In there, somewhere.
SAITO: For someone like you to steal?
ARTHUR: Yes. In the dream state, conscious defenses are lowered and your thoughts become vulnerable to theft. It's called extraction.
COBB: But, Mr. Saito, we can train your subconscious to defend itself from even the most skilled extractor.
SAITO: How can you do that?
COBB: Because I am the most skilled extractor. I know how to search your mind and find your secrets. I know the tricks, and I can teach them to your subconscious so that even when you're asleep, your guard is never down.
MAL: If I jumped, would I survive?
COBB: With a clean dive, perhaps. Mal, why are you here?
MAL: I thought you might be missing me...
COBB: I am. But I can't trust you anymore.
MAL: So what?