20 Things You Somehow Missed In Shutter Island
5. The Law Of Four
The mystery of Rachel's "disappearance" is propelled into motion by a cryptic note she left behind, reading, "The law of 4. Who is 67?"
In reality of course the note is simply part of the role-play intended to lead Teddy to break his delusions and embrace his real identity as Andrew, something that's very sneakily hinted at mid-way through the story.
When Teddy attends an Ashecliffe staff meeting held by Dr. Cawley, he inquires with Cawley about the note left by Rachel, at which point Scorsese cuts to a staff member at the meeting who off-handedly tells a colleague, "The law of four. I love that."
It's such a quick moment spliced into the scene, and one that many might not even catch, yet once the twist is known, it's clearly further proof that everything we're seeing is part of a controlled fabrication which all the staff members are aware of.